Seagate ELITE 9 Product Manual

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Elite 9 Disc Drive

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ST410800N/ND

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ST410800W/WD

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Product Manual, Volume 1

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Elite 9 Disc Drive

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

ST410800N/ND

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

ST410800W/WD

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

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

Product Manual, Volume 1

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

© 1994 Seagate Technology, Inc. All rights reserved
Publication number: 83328860, Rev. C
September 1994

Seagate®, Seagate Technology®, and the Seagate logo are registered
trademarks of Seagate Technology, Inc. Elite™, SeaFAX™, SeaFONE™,
SeaTDD™, and SeaBOARD™ are trademarks 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) 10/30/93 L. Newman/L. Clausen All
A 12/10/93 L. Newman/L. Clausen All
B 05/18/94 L. Newman/L. Clausen All
C (preliminary-01) 07/21/94 L. Newman/L. Clausen All
C 09/23/94 L. Newman/L. Clausen 26, 41

Note. Product Manual 83328860 is Volume 1 of a two-volume

document with the SCSI interface information in the

SCSI-2 Interface Product Manual,

Part Number 77738479.

Volume 2

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 ................................................................................................................. 8

4.1.1 Reliability ............................................................................................................. 8

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

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

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

5.0 Performance-related characteristics and features ......................................................... 11

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

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

5.2.1 Seek time ............................................................................................................ 12

5.2.2 Format drive command execution time................................................................ 12

5.3 General performance characteristics ............................................................................ 13

5.4 Start/stop time............................................................................................................... 13

5.5 Prefetch/multi-segmented cache control ....................................................................... 14

5.5.1 Adaptive read lookahead..................................................................................... 15

5.6 Caching write data ........................................................................................................ 15

5.7 Synchronized spindle operation .................................................................................... 16

6.0 Reliability specifications................................................................................................... 19

6.1 Error rates..................................................................................................................... 19

6.1.1 Environmental interference.................................................................................. 19

6.1.2 Write errors ......................................................................................................... 19

6.1.3 Seek errors ......................................................................................................... 20

6.2 Reliability and service ................................................................................................... 20

6.2.1 Mean time between failures (MTBF).................................................................... 20

6.2.2 Air flow ................................................................................................................ 20

6.2.3 Preventive maintenance ...................................................................................... 23

6.2.4 Service life........................................................................................................... 23

6.2.5 Service philosophy .............................................................................................. 23

6.2.6 Installation ........................................................................................................... 23

6.2.7 Service tools........................................................................................................ 23

vi Elite 9 Product Manual, Rev. C

7.0 Physical and electrical specifications............................................................................ 25

7.1 AC power requirements ............................................................................................ 25

7.2 DC power requirements ............................................................................................ 25

7.2.1 Conducted noise immunity ............................................................................ 27

7.2.2 Power sequencing......................................................................................... 27

7.2.3 +12V current profile ....................................................................................... 28

7.3 Heat/power dissipation.............................................................................................. 28

7.4 Environmental limits.................................................................................................. 29

7.4.1 Temperature.................................................................................................. 29

7.4.2 Relative humidity ........................................................................................... 29

7.4.3 Effective altitude (sea level)........................................................................... 29

7.4.4 Shock and vibration ....................................................................................... 29

7.4.5 Air cleanliness ............................................................................................... 31

7.4.6 Acoustics....................................................................................................... 31

7.5 Electromagnetic compatibility.................................................................................... 31

7.6 Mechanical specifications ......................................................................................... 32

7.6.1 Drive orientation ............................................................................................ 33

7.6.2 Cooling .......................................................................................................... 33

8.0 Media characteristics ...................................................................................................... 35

8.1 Media description...................................................................................................... 35

9.0 Defect and error management ........................................................................................ 37

9.1 Defects and errors .................................................................................................... 37

10.0 Option headers ................................................................................................................ 39

10.1 ST410800 option headers......................................................................................... 39

10.2 Synchronized spindles interface ............................................................................... 42

10.2.1 Electrical description...................................................................................... 42

10.3 Grounding................................................................................................................. 43

11.0 Interface requirements .................................................................................................... 45

11.1 General description................................................................................................... 45

11.2 SCSI interface messages supported......................................................................... 45

11.3 SCSI interface commands supported........................................................................ 46

11.3.1 Inquiry data.................................................................................................... 48

11.3.2 Mode sense data ........................................................................................... 49

11.4 SCSI bus conditions and miscellaneous features supported..................................... 51

11.5 Synchronous data transfer........................................................................................ 52

11.5.1 Synchronous data transfer periods supported .............................................. 52

11.5.2 REQ/ACK offset............................................................................................ 52

11.6 DC cable and connector ........................................................................................... 52

Elite 9 Product Manual, Rev. C vii

11.7 SCSI physical interface............................................................................................. 53

11.7.1 Physical characteristics ................................................................................ 54

11.7.2 Connector requirements ............................................................................... 55

11.7.3 Electrical description..................................................................................... 55

11.8 SCSI physical interface............................................................................................. 59

11.8.1 Non-wide SCSI interface............................................................................... 59

11.8.2 Wide SCSI interface...................................................................................... 62

11.9 Disc drive SCSI timing .............................................................................................. 65

Index.......................................................................................................................................... 67

Figures

Figure 1. Elite 9 family disc drive .............................................................................................. 1

Figure 2. Elite 9 disc drive (exploded view)............................................................................... 5

Figure 3. OEM interruptible thermal calibration implementation ................................................ 12

Figure 4. Synchronized drive interconnect diagram .................................................................. 16

Figure 5. Synchronized reference signal characteristics........................................................... 17

Figure 6. Air-flow patterns......................................................................................................... 21

Figure 7. R/T/U/CYHX temperature measurement locations .................................................... 22

Figure 8. Elite 9 drive typical +12V current profile..................................................................... 28

Figure 9. Elite 9 drive typical mounting configuration dimensions ............................................. 32

Figure 10. Elite 9 drive recommended mounting......................................................................... 33

Figure 11. ST410800 option header locations ............................................................................ 39

Figure 12. Option select jumper connectors ............................................................................... 40

Figure 13. SCSI reference index signal driver/receiver combination........................................... 42

Figure 14. ST410800 configuration select header specification .................................................. 43

Figure 15. ST410800N/ND physical interface............................................................................. 53

Figure 16. ST410800W/WD physical interface ........................................................................... 53

Figure 17. Single-ended transmitters and receivers.................................................................... 56

Figure 18. Typical differential I/O line transmitter/receiver and terminators................................. 57

Figure 19. Terminating resistor locations for ND and WD drives ................................................ 58

Figure 20. Non-shielded non-wide SCSI device connector ......................................................... 59

Figure 21. Non-shielded wide SCSI device connector ................................................................ 62

Tables

Table 1. DC power requirements for ST410800N/ND drives ................................................... 25

Table 2. DC power requirements for ST410800W/WD drives.................................................. 26

viii Elite 9 Product Manual, Rev. C

Table 3. SCSI messages supported ........................................................................................ 45

Table 4. Supported commands............................................................................................... 46

Table 5. Elite 9 family drives inquiry data................................................................................. 48

Table 6. Mode sense data, Elite 9 default values (SCSI-1 implementation)............................. 49

Table 7. Mode sense data, Elite 9 default values (SCSI-2 implementation)............................. 50

Table 8. SCSI bus conditions and other miscellaneous features ............................................. 51

Table 9. Synchronous data transfer periods ............................................................................ 52

Table 10. Single-ended cable pin assignments ......................................................................... 60

Table 11. Differential cable pin assignments ............................................................................. 61

Table 12. Single-ended P cable pin assignments ...................................................................... 63

Table 13. Differential P cable pin assignments .......................................................................... 64

Table 14. Disc drive SCSI timing ............................................................................................... 65

Elite 9 Product Manual, Rev. C 1

1.0 Scope

This manual describes Seagate Technology®, Inc. Elite 9™ disc drives.
Elite 9 drives support the small computer system interface-2 (SCSI-2) as

described in the ANSI SCSI and SCSI-2 interface speci fications to the
extent described in this manual. The
(part number 77738479) describes general SCSI interface characteristics
of this and other families of Seagate drives

SCSI-2 Interface Product Manu al

Figure 1. Elite 9 family disc drive

2 Elite 9 Product Manual, Rev. C

Elite 9 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 parts, such as the Elite 9
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 Elite 9 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 Elite 9 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

Elite 9 Installation Guide

Seagate part number: 83328850

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 Elite 9 Product Manual, Rev. C

Elite 9 Product Manual, Rev. C 5

3.0 General description

Elite 9 drives are high capacity, high-performance, highly reliable random­access storage devices designed to meet the needs of the original equip­ment manufacturer (OEM) marketplace.

Elite 9 disc drives have an embedded SCSI controller. Performance informa­tion is provided in Section 5.

The Elite 9 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. Elite 9 disc drive (exploded view)

6 Elite 9 Product Manual, Rev. C

Elite 9 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.

Elite 9 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.

Elite 9 Product Manual, Rev. C 7

4.0 Standard features

Elite 9 drives have the following standard features:

• Integrated SCSI controller

• Single-ended or differential SCSI drivers and receivers

• Non-shielded 50-pin connector

• Initiator/target terminator power option

• SCSI bus parity with full parity pass-through

• SCSI disconnect/reconnect support

• Multiple SCSI initiator support

• SCSI-2 command set support

• Synchronous SCSI bus data transfer protocol (maximum offset of 15)

• 10.0 Mbytes/sec SCSI bus transfers (minimum period 100 nsec)

• 20.0 Mbytes/sec SCSI bus wide transfers (ST410800W/WD models)

• 954 Kbyte data buffer

• Cache buffer management

• User-selectable logical block size (180 to 4,096 bytes)

at even-number intervals

• ECC (error correction code) on the fly

• User-selectable automatic defect reallocation scheme

• User-selectable number of spare sectors per cylinder

• Industry standard 5.25-inch full-high form factor dimensions

(3.25 high × 5.75 wide × 8.00 deep)

• Microcode downloadable using the Write Data Buffer command

• Asynchronous and synchronous data-transfer protocols

• Firmware downloadable using a SCSI interface

• Programmable sector-reallocation scheme

• Flawed sector reallocation at format time

• Programmable auto-write and auto-read reallocation

• Reallocation of defects on command (Reassign Block command)

• 96-bit and 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 internal termination (ST410800N/W models)

8 Elite 9 Product Manual, Rev. C

4.1 Performance

• Programmable multi-segmentable cache buffer

• 5,400 RPM spindle; average latency = 5.55 msec

• Command queuing of up to 64 commands

• Background processing of queue

• Supports start and stop commands

• Provides synchronized spindle capability

• Low audible noise for office environment

• Low power consumption

4.1.1 Reliability

• 500,000 hour MTBF

• Adaptive seek velocity; improved seek performance

• LSI circuitry

• Balanced low-mass rotary voice-coil actuator

4.2 Unformatted and formatted capacities

Standard OEM models are formatted to have 512-byte sectors.
Elite 9 drives have one (1) spare cylinder per unit and 9 spare sectors per

cylinder. You may select the number of spare sectors per cylinder to meet
your specific needs.

Formatted Unformatted

9,090 Mbytes 10,800 Mbytes

Users having the necessary equipment may modify 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

4.3 Options

The following options are incorporated at the time of production or are
available separately. All kits may be installed in the field.

• Front panel
The standard front panel is black plastic; you may order other colors. The

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

Front panel kit with green lens, part number 70553702
Front panel kit with red lens, part number 705537012

• Two pin shunt jumpers, 2 mm, part number 97630051

• External terminator, single-ended, shielded, part number 15387797

• External terminator, single-ended, unshielded, part number 15387807

• Internal terminator, differential, part number 15479501

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

against transit damage. Units shipped individually require a dditional
protection as provided by the single-unit shipping pack. Users planning
single-unit distribution should specify this option.

(part number 77738479).

Elite 9 Product Manual, Rev. C 9

• Shielded SCSI I/O cable

1.5 foot cable, part number 47191159
5 foot cable, part number 47191151
15 foot cable, part number 47191152
20 foot cable, part number 47191153
40 foot cable, part number 47191164
80 foot cable, part number 47191154

•

Elite 9 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.

part number 83328850

4.4 Installation

For option jumper locations and definitions refer to Section 10. 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. ST410800N and ST410800W drives have termination built in
(ensure that the internal terminator has not been disconnected—see
Section 10.1 for termination options). ST410800ND and ST410800WD
drives are terminated internally with terminators in the sockets provided
next to the SCSI I/O connector. The terminator part number is 15479501.

• 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. To remove (disconnect) termination from ST410800N and
ST410800W drives, remove the jumper from pins 19 and 20 of J4A (see
Figure 12). To remove termination from ST410800ND and ST410800WD
drives, remove the terminators from the sockets located next to the SCSI
I/O connector (see Section 11.7.3.3).

• Set all appropriate option jumpers before 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 Elite 9 Product Manual, Rev. C

Elite 9 Product Manual, Rev. C 11

5.0 Performance-related characteristics
and features

This section provides performance-related characteristics and features of
Elite 9 drives.

5.1 Internal drive characteristics

Drive capacity, Mbytes unformatted 10,800
Read/write data heads 27
Bytes per track, average 77,700
Bytes per surface, Mbytes unformatted 400
Cylinders/tracks per surface, user accessible 4,925
Tracks per inch 3,921
Servo heads 1
Internal data rate, Mbits/sec, variable with zone 44 to 65
Disc rotation speed 5,400 ± 0.5%
Average rotational latency, msec 5.55

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-bloc k 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 Section 11.9 and to the
number 77738479) for additional timing details.

SCSI-2 Interface Product Manual

(part

12 Elite 9 Product Manual, Rev. C

Start

Has

10 min.

timer

expired?

Set

10 minute

timer

Yes

No

Yes

A

Is

SCSI

command in

progress?

No

Complete
Command

Seek to

TCAL cyl
and select
head zero

TCAL

head

Has

target

received a SCSI

command?

No

Yes

All

heads

calibrated?

Yes

A

All

heads

calibrated?

No

Yes

Select

next

head

No

Has

target

received a SCSI

command?

Yes

No

Target

completes

SCSI

command

Seek to

TCAL cyl
and select
next head

Figure 3. OEM interruptible thermal calibration implementation

5.2.1 Seek time

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

Avg typical** 11 12 12.5 13.5
Single track typ** 0.9 1.7 2.4 3.2
Full stroke typ** 23 24 24.5 25.5

* Measured from the start of the first sector transfer to or from the host.
** 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

≥≥

≥ 512-byte sectors

≥≥

for

Maximum (with verify) 4 hours
Maximum (without verify) 2 hours

Drive including
controller overhead

Elite 9 Product Manual, Rev. C 13

5.3 General performance characteristics

Minimum sector interleave 1:1
Data buffer to/from disc media 960 Kbytes
Data transfer rate (≤ 1 sector)

Minimum 5.67 Mbytes/sec*
Maximum 8.3 Mbytes/sec*

Data transfer rate (< 1 track)
Minimum, divided by interleave factor 4.75 Mbytes/sec
Maximum, divided by interleave factor 6.46 Mbytes/sec

SCSI interface data
Asynch. transfer rate non-wide, max instantaneous 10 Mbytes/sec*, **
Asynch. transfer rate wide, max instantaneous 20 Mbytes/sec*, ***
Synchronous transfer rate fast 0.5 to 10 Mbytes/sec
Synchronous transfer rate wide 5.0 to 20 Mbytes/sec

Sector size
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 0.8 msec
Overhead time for one-track cylinder switch 1.8 msec (typical)
Average rotational latency 5.55 msec
* Rate measured from the s tart of the fi rst sector transfer to or from the host.

** Assumes system ability to support 10 Mbytes/sec and no cable loss.
***Assumes system ability to support 20 Mbytes/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
(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

SCSI-2 Interface Product Manual

SCSI-2 Interface Product Manual

(77738479) less

).

There is no power control switch on the drive.

14 Elite 9 Product Manual, Rev. C

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, approximately 960 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 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 se gment of the c ache. The d rive
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 0 2h (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

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

SCSI-2 Interface Product Manual

).

).

).

SCSI-2 Inter-

Elite 9 Product Manual, Rev. C 15

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. De fault 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 1 to 16. Divide the 960 bytes in the buffer by the
number of segments to get the segment size; default is 3 segments (see the

SCSI-2 Interface Product Manual

individual segments greatly enhances the cache’s overall performance,
allowing a wide range of user-select able configurations including a pure
prefetch strategy.

).

). The wrap-around capability of the

SCSI-2 Interface

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
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.

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

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.

SCSI-2 Interface Product Manual

).