seagate ST11950N, ST11950ND, ST11950WD, ST12550W, ST12550WD Product Manual

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Barracuda 1 and 2 Disc Drive

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ST11950N/ND, ST11950W/WD

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ST12550N/ND, ST12550W/WD

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Product Manual, Volume 1

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Barracuda 1 and 2 Disc Drive

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ST11950N/ND, ST11950W/WD,

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ST12550N/ND, ST12550W/WD

○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○

Product Manual, Volume 1

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Seagate®, Seagate Technology®, and the Seagate logo are registered trademarks of Seagate Technology, Inc. Barracuda™ is a trademark of Seagate Technology, Inc. Other product names are registered trademarks or trademarks of their owners.

Seagate reserves the right to change, without notice, product offerings or specifications. No part of this publication may be reproduced in any form without written permission from Seagate Technology, Inc.

Revision status summary sheet

Sheets

Revision Date Writer/Engineer Affected

A (preliminary-01) 04/05/93 L. Newman/J. Olson All A (preliminary-02) 04/20/93 L. Newman/J. Olson All A (preliminary-03) 05/01/93 L. Newman/J. Olson All A 05/11/93 L. Newman/J. Olson All B (preliminary-01) 09/15/93 L. Newman/J. Olson All B 10/18/93 L. Newman/J. Olson All C (draft) 10/11/94 L. Newman/J. Olson All C 11/04/94 L. Newman/J. Olson All

Note. Product Manual 83327780 is Volume 1 of a two-volume

document with the SCSI interface information in the Volume 2 SCSI-2 Interface Product Manual, part number 77738479.

Barracuda 1 and 2 Product Manual, Rev. C v

Contents

1.0 Scope ................................................................................................................................. 1

2.0 Applicable standard and reference documentation ....................................................... 3

2.1 Standards ..................................................................................................................... 3

2.2 Applicable reference documents................................................................................... 3

3.0 General description........................................................................................................... 5

4.0 Standard features.............................................................................................................. 7

4.1 Performance ................................................................................................................. 7

4.1.1 Reliability ............................................................................................................. 7

4.2 Unformatted and formatted capacities .......................................................................... 8

4.3 Options ......................................................................................................................... 8

4.4 Installation..................................................................................................................... 9

5.0 Performance characteristics ............................................................................................ 11

5.1 Internal drive characteristics ......................................................................................... 11

5.2 SCSI seek performance characteristics ........................................................................ 11

5.2.1 Seek time ............................................................................................................ 13

5.2.2 Format drive command execution time................................................................ 13

5.3 General performance characteristics ............................................................................ 14

5.4 Start/stop time............................................................................................................... 14

5.5 Prefetch/multi-segmented cache control ....................................................................... 15

5.5.1 Adaptive read lookahead..................................................................................... 16

5.6 Caching write data ........................................................................................................ 16

5.7 Synchronized spindle operation .................................................................................... 17

6.0 Reliability specifications................................................................................................... 21

6.1 Error rates..................................................................................................................... 21

6.1.1 Environmental interference.................................................................................. 21

6.1.2 Write errors ......................................................................................................... 21

6.1.3 Seek errors ......................................................................................................... 22

6.2 Reliability and service ................................................................................................... 22

6.2.1 Mean time between failures (MTBF).................................................................... 22

6.2.2 Air flow ................................................................................................................ 22

6.2.3 Preventive maintenance ...................................................................................... 28

6.2.4 Service life........................................................................................................... 28

6.2.5 Service philosophy .............................................................................................. 28

6.2.6 Installation ........................................................................................................... 28

6.2.7 Service tools........................................................................................................ 28

6.2.8 Hot plugging Barracuda 1 and 2 disc drives ........................................................ 28

vi Barracuda 1 and 2 Product Manual, Rev. C

7.0 Physical/electrical specifications ................................................................................... 31

7.1 AC power requirements ............................................................................................ 31

7.2 DC power requirements ............................................................................................ 31

7.2.1 Conducted noise immunity ............................................................................ 33

7.2.2 Power sequencing......................................................................................... 33

7.2.3 12V current profile ......................................................................................... 34

7.3 Heat/power dissipation.............................................................................................. 35

7.4 Environmental limits.................................................................................................. 35

7.4.1 Temperature.................................................................................................. 35

7.4.2 Relative humidity ........................................................................................... 35

7.4.3 Effective altitude (sea level)........................................................................... 36

7.4.4 Shock and vibration ....................................................................................... 36

7.4.5 Air cleanliness ............................................................................................... 37

7.4.6 Acoustics....................................................................................................... 37

7.5 Electromagnetic compatibility.................................................................................... 37

7.6 Mechanical specifications ......................................................................................... 38

7.6.1 Drive orientation ............................................................................................ 40

7.6.2 Cooling .......................................................................................................... 40

8.0 Media characteristics ...................................................................................................... 41

8.1 Media description...................................................................................................... 41

9.0 Defect and error management ........................................................................................ 43

9.1 Defects and errors .................................................................................................... 43

10.0 Option/configuration headers......................................................................................... 45

10.1 Drive ID/option select headers .................................................................................. 45

10.1.1 ST11950N/ND and ST12550N/ND configuration ........................................... 45

10.1.2 ST11950W/WD and ST12550W/WD configuration ........................................ 48

10.2 Synchronized spindles interface ............................................................................... 50

10.2.1 Electrical description...................................................................................... 50

10.3 Grounding................................................................................................................. 52

11.0 Interface requirements .................................................................................................... 53

11.1 General description................................................................................................... 53

11.2 SCSI interface messages supported......................................................................... 53

11.3 SCSI interface commands supported........................................................................ 54

11.3.1 Inquiry data.................................................................................................... 56

11.3.2 Mode sense data ........................................................................................... 56

11.4 SCSI bus conditions and miscellaneous features supported..................................... 61

11.5 Synchronous data transfer........................................................................................ 62

Barracuda 1 and 2 Product Manual, Rev. C vii

11.5.1 Synchronous data transfer periods supported .............................................. 62

11.5.2 REQ/ACK offset............................................................................................ 63

11.6 DC cable and connector ........................................................................................... 63

11.7 SCSI physical interface............................................................................................. 63

11.7.1 Physical characteristics ................................................................................ 64

11.7.2 Connector requirements ............................................................................... 65

11.7.3 Electrical description..................................................................................... 66

11.8 SCSI non-wide physical interface ............................................................................. 70

11.9 SCSI wide physical interface..................................................................................... 73

11.10Disc drive SCSI timing .............................................................................................. 76

Index.......................................................................................................................................... 79

Figures

1 Barracuda 1 and 2 family disc drives ................................................................................ 1

2 Barracuda disc drive (exploded view) ............................................................................... 5

3 OEM interruptible thermal compensation implementation .................................................12

4 Synchronized drive interconnect diagram ......................................................................... 17

5 Synchronized reference signal characteristics .................................................................. 18

6 Air-flow pattern .................................................................................................................. 23

7 TYFX temperature measurement locations....................................................................... 24

8 UYFX temperature measurement locations ...................................................................... 25

9 TYGX temperature measurement locations ......................................................................26

10 PYGX temperature measurement locations ...................................................................... 27

11 Temperature measurement location .................................................................................27

12 Barracuda 1 and 2 drives typical +12V current profiles ..................................................... 34

13 Mounting configuration dimensions for N/ND drives.......................................................... 38

14 Mounting configuration dimensions for W/WD drives ........................................................ 39

15 Recommended mounting .................................................................................................. 40

16 ST11950N/ND and ST12550N/ND physical interface ....................................................... 45

17 ST11950N/ND and ST12550N/ND jumper connectors ..................................................... 46

18 ST11950W/WD and ST12550W/WD physical interface .................................................... 48

19 ST11950W/WD and ST12550W/WD jumper connectors .................................................. 48

20 SCSI reference index signal driver/receiver combination .................................................. 50

21 ST11950N/ND and ST12550N/ND configuration select header specification.................... 51

22 ST11950W/WD and ST12550W/WD configuration select header specification ................ 51

23 ST11950N/ND and ST12550N/ND physical interface ....................................................... 63

24 ST11950W/WD and ST12550W/WD physical interface .................................................... 64

viii Barracuda 1 and 2 Product Manual, Rev. C

25 Single-ended transmitters and receivers...........................................................................67

26 Typical differential I/O line transmitters/receivers and terminators .................................... 68

27 Non-shielded SCSI device connector................................................................................70

28 Wide SCSI device connector ............................................................................................73

Tables

1 DC power requirements for ST11950N/ND and ST12550N/ND drives ............................. 31

2 DC power requirements for ST11950W/WD and ST12550W/WD drives .......................... 32

3 SCSI messages supported ............................................................................................... 53

4 Supported commands.......................................................................................................54

5 Barracuda 1 and 2 family drive inquiry data ...................................................................... 56

6 Mode Sense data, ST11950 default values (SCSI-1 implementation)...............................57

7 Mode Sense data, ST11950 default values (SCSI-2 implementation)...............................58

8 Mode Sense data, ST12550 default values (SCSI-1 implementation)...............................59

9 Mode Sense data, ST12550 default values (SCSI-2 implementation)...............................60

10 SCSI bus conditions and other miscellaneous features ....................................................61

11 Synchronous data transfer periods for ST11950N/ND and ST12550N/ND drives............. 62

12 Synchronous data transfer periods for ST11950W/WD and ST12550W/WD drives.......... 62

13 Single-ended cable pin assignments (non-shielded connector)

for ST11950N and ST12550N drives ................................................................................ 71

14 Differential cable pin assignments (non-shielded connector)

for ST11950ND and ST12550ND drives ........................................................................... 72

15 Single-ended contact assignments (P cable) for ST11950W and ST12550W drives ........ 74

16 Single-ended contact assignments (P cable) for ST11950WD and ST12550WD drives ...75

17 Disc drive SCSI timing ...................................................................................................... 76

Barracuda 1 and 2 Product Manual, Rev. C 1

N/ND type

W/WD type

1.0 Scope

This manual describes Seagate Technology®, Inc. Barracuda™ 1 and 2 disc drives.

Barracuda drives support the small computer system interface-2 (SCSI-2) as described in the ANSI SCSI and SCSI-2 interface specifications to the extent desc ribed in this manual. The (part number 77738479) describes general SCSI interface characteristics of this and other families of Seagate drives.

ST11950N/ND and ST11950W/WD drives are classified as Barracuda 1 family drives. ST12550N/ND and ST12550W/WD drives are classified as Barracuda 2 family drives.

SCSI-2 Interface Product Manual

Figure 1. Barracuda 1 and 2 family disc drives

2 Barracuda 1 and 2 Product Manual, Rev. C

Barracuda 1 and 2 Product Manual, Rev. C 3

2.0 Applicable standard and reference documentation

Seagate takes all reasonable steps to ensure that its products are certifiable to currently accepted standards. Typical applications of these disc drives include customer packaging and subsystem design.

Safety agencies conditionally certify component assemblies, such as the Barracuda disc drive, based on their final acceptability in the end-use product. The subsystem designer is responsible for meeting these conditions of acceptability in obtaining safety/regulatory agency compliance in their end-use product and certifying where required by law.

2.1 Standards

The Barracuda disc drive is a UL recognized component per UL1950, CSA certified to CSA C22.2 No. 950-M89, and VDE certified to VDE 0805 and EN60950.

The Barracuda disc drive is supplied as a component part. It is the responsibility of the subsystem designer to meet EMC/regulatory requirements. Engineering test characterizations of radiated emissions are available from the Seagate safety department.

2.2 Applicable reference documents

Barracuda Disc Drive Installation Guide

Seagate part number: 83327770

SCSI-2 Interface Product Manual (volume 2)

Seagate part number: 77738479

ANSI small computer system interface (SCSI) documents

ANSI X3.131-1986 (SCSI-1) X3T9.2/86-109 Rev. 10H (SCSI-2) X3T9.2/91-010 Rev. 10 (SCSI-3) Parallel Interface

In case of conflict between this document and any referenced document, this document takes precedence.

4 Barracuda 1 and 2 Product Manual, Rev. C

Barracuda 1 and 2 Product Manual, Rev. C 5

3.0 General description

Barracuda drives are low-cost, high-performance, random-access storage devices designed to meet the needs of the original equipment manufacturer (OEM) marketplace.

The Barracuda drive’s interface supports multiple initiators, disconnect/ reconnect, self-configuring host software, and automatic features that relieve the host from knowing the physical characteristics of the targets (logical block addressing is used).

The head and disc assembly (HDA) is sealed at the factory. Air circulates within the HDA through a non-replaceable filter to maintain a contaminationfree HDA environment.

Refer to Figure 2 for an exploded view of the drive. This exploded view is for information only—never disassemble the HDA and do not attempt to service items in the sealed enclosure (heads, media, actuator, etc.) as this requires special facilities. The drive contains no replaceable parts. Opening the HDA voids your warranty.

Figure 2. Barracuda disc drive (exploded view)

6 Barracuda 1 and 2 Product Manual, Rev. C

Barracuda drives use a dedicated landing zone at the innermost radius of the media to eliminate the possibility of destroying or degrading data by landing in the data zone. The drive automatically goes to the landing zone when the power is removed.

An automatic shipping lock prevents potential damage to the heads and discs. The shipping lock disengages when power is applied to the drive and the head load process begins.

Barracuda drives decode track 0 location data from the dedicated servo surface to eliminate mechanical transducer adjustments and related reliability concerns.

A high-performance actuator assembly with a low-inertia, balanced, patented, straight-arm design provides excellent performance with minimal power dissipation.

Barracuda 1 and 2 Product Manual, Rev. C 7

4.0 Standard features

Barracuda 1 and 2 drives have the following standard features:

• Integrated SCSI controller

• Single-ended or differential SCSI drivers and receivers

• Asynchronous and synchronous data-transfer protocols

• Firmware downloadable using a SCSI interface

• Selectable sector size from 180 to 4,096 bytes per sector

• Programmable sector-reallocation scheme

• Flawed sector reallocation at format time

• Programmable auto-write and auto-read reallocation

• Reallocation of defects on command (post format)

• 96-bit Reed-Solomon error-correction code

• Sealed head and disc assembly (HDA)

• No preventive maintenance or adjustments required

• Dedicated head-landing zone

• Automatic shipping lock

• Automatic thermal compensation

• Embedded Grey Code track address to eliminate seek errors

• Self-diagnostics performed at power-on

• 1:1 interleave

• Zone bit recording (ZBR)

• Vertical, horizontal, or top-down mounting

• Dynamic spindle brake

• Active termination with removable terminator modules

• Synchronous spindle capability

• 1,024 Kbyte data buffer (N/ND/W models)

• 512 Kbyte data buffer (WD models)

• Low audible noise for office environment

• Low power consumption

4.1 Performance

• Programmable multi-segmentable cache buffer

• 7,200 RPM spindle; average latency = 4.17 msec

• Command queuing of up to 64 commands

• Background processing of queue

• Supports start and stop commands

• Provides synchronized spindle capability

• Adaptive seek velocity; improved seek performance

4.1.1 Reliability

• 500,000 hour MTBF

• LSI circuitry

• Balanced low-mass rotary voice-coil actuator

8 Barracuda 1 and 2 Product Manual, Rev. C

4.2 Unformatted and formatted capacities

Standard OEM models are formatted to have 512-byte sectors. The ST11950 drive has six (6) spare sectors per cylinder and one (1) spare

cylinder per unit. The ST12550 drive has nine (9) spare sectors per cylinder and one (1) spare

cylinder per unit.

Formatted Unformatted

ST11950N/ND 1,690 Mbytes 2,030 Mbytes ST11950W/WD 1,690 Mbytes 2,030 Mbytes ST12550N/ND 2,139 Mbytes 2,572 Mbytes ST12550W/WD 2,139 Mbytes 2,572 Mbytes

Users having the necessary equipment may modi fy the data block size before issuing a format command to obtain different formatted capacities. User-available capacity also depends on the spare reallocation scheme selected. See the Mode Select command and the Format command in the

SCSI-2 Interface Product Manual

(part number 77738479).

4.3 Options

The capacities shown in Section 4.2 are normally provided. Other capacities can be or dered de pending on the sparing scheme and sector size requested.

The following options are incorporated at the time of production or are available separately.

• Front panel (green lens), part number 70869751 The standard front panel is black plastic. You may order other colors. Each

panel has a single rectangular green LED indicator lens that, when glowing, indicates the drive is selected.

•

Barracuda Disc Drive Installation Guide,

This manual provides basic installation information for persons not familiar with the product. It also includes information on obtaining technical support and service for the drive.

• Drive termination for single-ended drives Removable resistor modules (SIPs) provide ST11950N and ST12550N

drive termination. Permanently mounted active terminator ICs provide ST11950W and ST12550W drive termination; however, the ICs may be disabled by removing the Enable Drive Terminator jumper from J4 pins 11 and 12. See Section 11.7.3.3.

• Single-unit shipping pack kit The drive is shipped in bulk packaging to provide maximum protection

against transit damage. Units shipped individually require additional protection as provided by the single-unit shipping pack.

• Adapter accessory frame kit, part number 75790701 This kit contains a frame, which allows a 3.5-inch drive to be mounted

in a 5.25-inch drive bay. It includes mounting hardware, front panel with a green lens, an LED with cable that connects to the remote LED connector, and installation instructions.

part number 83327770

Barracuda 1 and 2 Product Manual, Rev. C 9

4.4 Installation

For option jumper locations and definitions refer to Section 10.1. Drive default mode parameters are not normally needed for installation. Refer to Section 11.3.2 for default mode parameters if you need them.

• Ensure that the SCSI ID of the drive is not the same as the host adapter.

• If multiple devices are on the bus, set the drive’s SCSI ID to one that is not presently used by other devices on the bus.

• If the drive is the only device on the bus, attach it to the end of the SCSI bus cable. Internal termination is available on ST11950N, ST11950W, ST12550N, and ST12550W drives (see Sections 10.1 and 11.7.3.4).

External terminators are required for ST11950ND, ST11950WD, ST12550ND, and ST12550WD drives. These external terminators must be provided by the user, systems integrator, or host equipment manufacturer.

• If you attach the drive to a bus that contains other devices, and the new drive is not attached to the end of the bus, remove termination from the new drive.

• Set all appropriate option jumpers prior to applying power to the drive. If you change jumpers after applying power, recycle the drive’s power to make the new settings effective.

Formatting

• It is not necessary to low-level format this drive. The drive is shipped from the factory low-level formatted in 512-byte sectors.

• Reformat the drive if: a. You select a different sector size.

b. You select a different spare-sector allocation scheme.

10 Barracuda 1 and 2 Product Manual, Rev. C

Barracuda 1 and 2 Product Manual, Rev. C 11

5.0 Performance characteristics

This section provides performance-related characteristics and features of Barracuda 1 and 2 drives.

5.1 Internal drive characteristics

ST11950 ST12550

Drive capacity, Mbytes unformatted 2,030 2,572 Read/write data heads, maximum 15 19 Bytes per track, average 49,768 49,768 Bytes per surface, Mbytes unformatted 135.7 135.7 Cylinders/tracks per surface, 2,706 2,707

user accessible Tracks per inch 3,047 3,047 Bits per inch 52,187 52,187 Servo heads 1 1 Internal data rate 34.3 to 56.5 34.3 to 56.5

Mbits/sec, variable with zone Disc rotation speed 7,200 ± 0.5% 7,200 ± 0.5% Average rotational latency, msec 4.17 4.17

5.2 SCSI seek performance characteristics

All performance characteristics assume that automatic adaptive thermal compensation is not in process when the drive receives the SCSI command. Automatic adaptive thermal compensation will not interrupt an active SCSI command. If adaptive thermal compensation is in process when a SCSI command is received, the command is queued until compensation completes. When compensation completes for the head, the first queued SCSI command executes, and the drive continues compensation for the remaining head(s).

The above procedure continues until compensation for all heads has completed, or until 10 minutes have elapsed. The drive initiates an automatic adaptive thermal compensation cycle once on power-up before completing its initialization sequence, once after 1 minute from the end of initialization, and then once approximately every 10 minutes. Automatic thermal compensation occurs at other times but should be transparent to the user (e.g., during format, at Re-Zero command, at spindle-up, during read-error recovery, and during reassign-block functions). You can use the Re-Zero command to reset the thermal compensation timer to its start to let the host know when the interruption for thermal compensation will occur.

Refer to Table 17 in Section 11.10 and to the

Manual

(part number 77738479) for additional timing details.

SCSI-2 Interface Product

12 Barracuda 1 and 2 Product Manual, Rev. C

Start

Has

10 min.

timer

expired?

Set

10 minute

timer

Yes

Is

SCSI

command in

progress?

Complete Command

Seek to

TCAL cyl and select head zero

TCAL

head

Has

target

received a SCSI

command?

Yes

All

heads

calibrated?

Yes

All

heads

calibrated?

Yes

Select

next

head

Has

target

received a SCSI

command?

Yes

Target

completes

SCSI

command

Seek to

TCAL cyl and select next head

Figure 3. OEM interruptible thermal compensation implementation

Barracuda 1 and 2 Product Manual, Rev. C 13

5.2.1 Seek time

Drive including controller overhead

Drive level (msec) without disconnect (msec) read write read write

Average typical* 8.0 9.0 9.0 10.0 Single track typical* 0.6 0.9 1.6 1.9 Full stroke typical* 17 19 18.0 20.0

*Typical seek values are measured under nominal conditions of tempera-

ture, voltage, and horizontal orientation on a representative sample of drives.

5.2.2 Format drive command execution time

≥≥

for

≥ 512-byte sectors

≥≥

ST11950 ST12550

Maximum (with verify) 30 minutes 37 minutes Maximum (without verify) 18 minutes 22 minutes

14 Barracuda 1 and 2 Product Manual, Rev. C

5.3 General performance characteristics

Minimum sector interleave 1 to 1 Data buffer to/from disc media 512-byte sector Data transfer rate (≤ 1 sector)

Minimum 4.28 Mbytes/sec* Maximum 7.06 Mbytes/sec*

Data transfer rate (< 1 track) Minimum 3.56 Mbytes/sec*

Maximum 5.96 Mbytes/sec* SCSI interface data

Asynchronous transfer rate * 5.0 Mbytes/sec** (non-wide) (maximum instantaneous) 10.0 Mbytes/sec*** (wide)

Synchronous transfer rate fast and wide 0.5 to 10 Mbytes/sec (ST11950N/ND and ST12550N/ND)

Synchronous transfer rate wide 5.0 to 20 Mbytes/sec (ST11950W/WD and ST12550W/WD)

Sector sizes Default 512-byte data blocks

Variable in even-sector sizes 180 to 4,096 bytes Read/write consecutive sectors on a track Yes Flaw reallocation performance impact

Spare sectors per track reallocation Negligible Spare sectors per cylinder reallocation Negligible Spare tracks per volume reallocation 35 msec (typical)

Overhead time for head switch 0.7 msec Overhead time for one-track cylinder switch 1.6 msec (typical) Average rotational latency 4.17 msec * Rate measured from the start of the first sector transfer to or from the host.

** Assumes system ability to support 5.0 Mtransfers/sec and no cable loss. ***Assumes system ability to support 5.0 Mtransfers/sec and no cable loss.

5.4 Start/stop time

Disabling the Motor Start option causes the motor to start as soon as power is applied, causing the drive to become ready within 30 seconds after DC power is applied at nominal voltage. If a recoverable error condition is detected during the start sequence, the drive executes a recovery procedure which may cause the drive to become ready in excess of 30 seconds. During the start sequence the drive responds to some commands over the SCSI interface. Stop time is less than 30 seconds (maximum) from removal of DC power.

Enabling the Motor Start option causes the internal controller to accept the commands listed in the than 3 seconds after applying DC power. After receiving the Motor Start command, the drive becomes ready for normal operation within 30 seconds

SCSI-2 Interface Product Manual

(77738479) less

Barracuda 1 and 2 Product Manual, Rev. C 15

(excluding the error recovery procedure). The Motor Start command can also be used to command the drive to stop the spindle (see the Start/Stop command information in the

There is no power control switch on the drive.

SCSI-2 Interface Product Manual

5.5 Prefetch/multi-segmented cache control

The drive provides a prefetch/multi-segmented cache algorithm, which in many cases enhances system performance. To select this feature, the host sends the Mode Select command with the proper values in the applicable bytes in page 08h (see the prefetch and cache operation enabled.

Of the 1,024 Kbytes physical buffer space in the ST11950N/ND/W and ST12550N/ND/W drives, approximately 960 Kbytes can be used as a cache. Of the 512 Kbytes physical buffer space in the ST11950WD and ST12550WD drives, approximately 480 Kbytes can be used as a cache. The cache can be divided into logical segments from which data is read and to which data is written.

The drive keeps track of the logical block addresses of the data stored in each segment of the cache. If the cache is enabled (see RCD bit, Table 5.2.1-27 in the

SCSI-2 Interface Product Manual),

read command is retrieved from the cache before any disc access is initiated. Data in contiguous logical blocks immediately beyond that requested by the Read command can be retrieved and stored in the cache for immediate transfer to the initiator on subsequent read commands. This is referred to as the prefetch operation. Since data that is prefetched may replace data already in the cache segment, an initiator can limit the amount of prefetch data to optimize system performance. The drive never prefetches more sectors than the number specified in bytes 8 and 9 of Mode page 08h (see the

SCSI-2 Interface Product Manual

Kbytes of the buffer (480 Kbytes for ST11950WD and ST12550WD drives) are used as a circular buffer for read/writes, with no prefetch operation and no segmented cache operation.

SCSI-2 Interface Product Manual

data requested by the host with a

). If the cache is not enabled, 960

). Default is

The following is a simplified description of the prefetch/cache operation: Case A. A read command is received and the first logical block is already in

the cache.

1. The drive transfers to the initiator the first logical block requested plus all subsequent contiguous logical blocks that are already in the cache. This data may be in multiple segments.

2. When a requested logical block is reached that is not in any segment, the drive fetches it and any remaining requested logical block addresses from the disc and puts them in a segment of the cache. The drive transfers the remaining requested logical blocks from the cache to the initiator in accordance with the “buffer-full” ratio specification given in Mode Select Disconnect/Reconnect parameters, page 02h (see the

SCSI-2 Interface Product Manual

3. The drive prefetches additional logical blocks contiguous to those transferred in step 2 above and stores them in the segment. The drive stops filling the segment when the maximum prefetch value has been transferred (see the

SCSI-2 Interface Product Manual

16 Barracuda 1 and 2 Product Manual, Rev. C

Case B. A read command is received and the first logical block address requested is not in any segment of the cache.

1. The drive fetches the requested logical blocks from the disc and transfers them into a segment, then from there to the initiator in accordance with the “buffer-full” ratio specification given in Mode Select Disconnect/Reconnect parameters, page 02h (see the

face Product Manual

2. The drive prefetches additional logical blocks contiguous to those transferred in Case A, step 2 above and stores them in the segment. The drive stops filling the segment when the maximum prefetch value has been transferred.

During a prefetch, the drive crosses a cylinder boundary to fetch data only if the Discontinuity (DISC) bit is set to 1 in bit 4 of byte 2 of the Mode Select parameters page 8h. Default is zero for bit 4 (see the

Product Manual

Each cache se gment i s actually a self-contained circular buffer whose length is an integer number of sectors. The drive supports operation with any integer number of segments from 1 to 16. Divide the 983,040 bytes (491,520 bytes for ST11950WD and ST12550WD drives) in the buffer by the number of segments to get the segment size; default is 3 segments (see the

2 Interface Product Manual

segments greatly enhances the cache’s overall performance, allowing a wide ran ge of user-selectable configurations including a pure prefetch strategy.

). The wraparound capability of the individual

SCSI-2 Inter-

SCSI-2 Interface

SCSI-

5.5.1 Adaptive read lookahead

Read lookahead causes the drive to continue reading data from the disc following a normal read I/O until the read-ahead parameters are satisfied (prefetch). If subsequent I/O requests can be satisfied from the prefetched data in the data buffer, there is a significant improvement in performance since a disc access is eliminated. If subsequent I/O requests cannot be satisfied from the prefetched data, there is a reduction in performance due to prefetch overhead.

The adaptive read lookahead feature suspends the prefetch operation if three subsequent read I/O requests are not satisfied from the prefetched data. This improves performance because unnecessary prefetches are avoided. Prefetch is reinstated if an I/O request is sequential to a previous I/O request.

5.6 Caching write data

Write caching is a drive-write operation, which uses a drive’s buffer storage area where data to be written to the disc is stored while the drive performs the Write command.

Write caching is enabled along with read caching. Default is cache enabled. For write caching, the same buffer space and segmentation is used as set up for read functions. When a write command is issued, the cache is first checked to see if any logical blocks to be written are already stored in the cache from a previous read or write command. If there are, the respective cache segments are cleared. The new data is cached for subsequent read commands.

Barracuda 1 and 2 Product Manual, Rev. C 17

Master Sync

Source

Host

(or other drive)

Spindle Control

Drive 1

+5V

1 2

Spindle Control

Drive 2

+5V

1 2

Spindle Control

Drive n

+5V

1 2

Sync Interface

System

Interface

If a 10-byte CDB write command (2Ah) is issued with the data page out (DPO) bit set to 1, no write data is cached, but the cache segments are still checked and cleared, if needed, for any logical blocks that are being written (see the

SCSI-2 Interface Product Manual

If the number of write data logical blocks exceeds the size of the segment being written into when the end of the segment is reached, data is written into the beginning of the same cache segment, overwriting data that was written there at the beginning of the operation. However, the drive does not overwrite data that has not yet been written to the disc.

5.7 Synchronized spindle operation

The synchronized spindle operation allows several drives operating from the same host to operate their spindles at the same synchronized rotational rate. Drives operating in a system in synchronized mode increase the system’s capacity and transfer rate in a cost-effective manner.

The interface consists of a twisted-pair cable, which connects the drives in the synchronized system in a daisy-chain configuration as shown in Figure 4.

Figure 4. Synchronized drive interconnect diagram

The host can reconfigure the drive any time after power-up to be the master or a slave by using the Mode Select command on the Rigid Disc Drive Geometry page. The master provides the reference signal to which all other drives phase-lock, including the master. There is only one master per system, and that can be a drive or the host computer. All drives may be configured as slaves allowing the host to provide the reference signal.

Each drive also can be configured for the non-synchronized mode in which it ignores any reference signal that might be present—this is the default mode as shipped from the factory. Connect the synchronized reference signal to the host only if the host provides the reference signal. If the host does not provide the reference signal, do not connect the host.

18 Barracuda 1 and 2 Product Manual, Rev. C

1.0 µsec min.

1.37 µsec max.

SSREF +

Rotational position locking Note. Mode Select page 4, byte 17, bits 1 and 0. RPL Description

00b Spindle synchronization is disabled (default value) 01b The target operates as a synchronized-spindle slave 10b The target operates as a synchronized-spindle master 11b The target operates as a synchronized-spindle master control

(not supported by the disc drive)

The VIC 2 LSI on the master drive provides the reference signal (SSREF+). The index signal g enerates a 120 Hz s ignal. The signal is normally false/negated (nominal 0V) and makes a transition to the true/asserted (nominal +5V) level to indicate the reference position during the revolution period. Master and slave drives use the trailing (falling) edge of the reference signal to phase-lock their spindles. A maximum of 10 seconds is allowed for a slave to synchronize with the reference signal. Figure 5 shows the characteristics of the reference signal.

Spindle synchronization input requirements:

SSREF +:Period (T) 0.0083 seconds (± 1.0% max)

Cycle-to-cycle variance: ± 10 microseconds Phase error while synchronized: ± 20 microseconds

Figure 5. Synchronized reference signal characteristics

SCSI interface factors

The Rotational Position Locking (RPL) field in byte 17 (bits 0 and 1) of the Rigid Disc Drive Geometry mode parameters page (page 04h) is used for enabling and disabling spindle synchronization mode (see the

Interface Product Manual

). If the target fails to synchronize, it creates a unit

SCSI-2

attention condition to all initiators. The sense key is set to Unit Attention and the additional sense code is set to Spindle Synchronized (5C01).

After reaching synchronization, if the target detects a change of synchronization and:

1. If the logical unit is not executing an I/O process for the initiator, then the target creates a unit attention condition. The sense key is set to Unit Attention and the additional sense code is set to Spindle Synchronized (5C01) or Spindle Not Synchronized (5C02).

2. If the logical unit is executing an I/O process and no other error occurs, then the target returns Check Condition status. The sense key is set to Recovered Error if the target is able to complete the I/O process or to Hardware Error if the target is unable to complete the I/O process. The additional sense code is set to Spindle Synchronized (5C01) or Spindle Not Synchronized (5C02).

Barracuda 1 and 2 Product Manual, Rev. C 19

You may operate the drive with a rotational skew when synchronized. The rotational skew is applied in the retarded direction (lagging the synchronizedspindle master control). A rotational offset of up to 255/256 of a revolution lagging may be selected. Select the amount of offset by using the Mode Select command, Rigid Disc Drive Geometry page (page 04h), byte 18 (see the

SCSI-2 Interface Product Manual

numerator of a fractional multiplier that has 256 as the denominator. For example, 40h selects 40h/FFh or 1/4 of a revolution lagging skew, 80h selects 1/2 of a revolution lagging skew, etc. Since the drive supports all offset values from 0 to 255, values sent by the initiator are not rounded off. The drive’s translation of the digital offset values to physical rotational offsets results in offset values whose phase error lies within the ± 20 microseconds phase error with respect to the supplied 120 Hz reference signal.

The drive does not have the capability to adjust the rotational offset value requested by the initiator to a physical offset in the drive that corresponds in any way to sector boundaries or changes in ZBR zones. The initiator must formulate these boundaries or changes, if required, to calculate the value of offset it sends to the drive.

). The value in byte 18 (0–FFh) is the

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