HP LTO 4 SAS, LTO 4 SCSI, LTO 4 FC User Manual

HP LTO Ultrium tape drives technical reference manual

LTO 4 FC, SCSI and SAS drives

volume 2: software integration

Edition 1, June 2007

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Legal and notice information

Hewlett-Packard Company makes no warranty of any kind with regard to this material, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose. Hewlett-Packard shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing, performance, or use of this material.

This document contains proprietary information, which is protected by copyright. No part of this document may be photocopied, reproduced, or translated into another language without the prior written consent of Hewlett-Packard. The information is provided “as is” without warranty of any kind and is subject to change without notice. The only warranties for HP products and services are set forth in the express warranty statements accompanying such products and services. Nothing herein should be construed as constituting an additional warranty. HP shall not be liable for technical or editorial errors or omissions contained herein.

Revision history

Version Edition Date Changes

LTO 4 1 June 2007 LTO 4 full-height drives

This document is frequently revised and updated. To find out if there is a later version, please ask your HP OEM Representative.

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1 Designing backup applications

In today’s computer market, software applications that use tape drives to copy the information from a computer’s hard disk for safe keeping are readily available for many different operating systems. Unfortunately, not all these applications take advantage of the advances made in tape technology over the past few years. This section examines some of the characteristics that a good backup utility should include.

Optimizing performance

There are some fundamental things that tape management applications should implement when dealing with Ultrium drives:

• Use large data transfer sizes.

• Control and monitor data compression.

• Ensure directory information is safe and accurate.

• Maximize the use of the tape drive’s internal buffering capability.

Each of these is discussed below.

For more information on optimizing performance, see “Factors affecting performance” on page 27.

Large data transfer size

Applications should use large data transfer sizes to make better use of the Ultrium drive’s internal buffers. A good goal to set is at least 128 KB each for read or write operation, with an ideal target of 256 KB:

• For fixed-length block mode reads and writes, provided the block size multiplied by the number

of blocks to be transferred is at least 128 KB, drives will provide peak performance. Small block sizes (512 bytes) are acceptable so long as they are written and read in fixed-length block mode using large transfers.

• For variable-length block mode reads and writes, the transfer length should be at least 256 KB.

Data compression control

Ultrium drives have built-in hardware data compression. Backup applications should incorporate features to report the actual compression ratio achieved during backup operations.

The typical compression ratio achieved during backup operations on PC and UNIX networks is 2:1, but this can vary widely depending on the actual data being compressed.

For more information, see “Controlling data compression” on page 51.

Non-immediate commands

Performance can be improved by only using immediate mode WRITE FILEMARKS commands.

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NOTE: Using immediate mode with other commands does not improve performance and can

cause problems when writing a driver. The SCSI specification requires that if a command is issued with the IMMEDIATE bit set to 0, the drive must flush its data buffer before it carries out the operation. This takes time.

Managing the use of tapes

The Ultrium format enables applications to monitor the performance of tapes closely, to indicate when tape heads need cleaning, and when a tape should be discarded.

See “Use of tapes” on page 19 for more information.

Information in Cartridge Memory

The LTO Cartridge Memory holds a number of pages of information that contain data about the tape’s history, such as the amount of data written to and read from the tape, the number of times a cartridge has been loaded and the tape threaded into a drive, and the number of read or write errors that have been encountered by drives with this tape. This information can be used to warn against backing up onto a tape of dubious quality, or one that is reaching the end of its life.

Cleaning tape heads

The ‘Clean’ LED on the front of HP Ultrium drives indicates when a cleaning cartridge should be used. There are two ways for backup applications to determine when the tape heads need cleaning and to prompt the user to clean the drive:

• Use TapeAlert—see “Monitoring the condition of the drive and media” on page 78 for details.

• Send a SCSI

the drive needs cleaning.

In an automation context, the tape drive tells the automation controller that a cleaning tape needs to be used through two bits in the ACI Get Drive Status command.

• The Cleaning Needed bit signals deterioration in the write or read margin of the drive and

indicates that a cleaning cartridge should be used as soon as possible. Once the drive has been cleaned successfully, the Cleaning Needed bit will be cleared.

• The Cleaning Required bit indicates that the drive is unable to read or write unless the drive is

first cleaned, so a cleaning cartridge should be used immediately. Following a successful clean, the Cleaning Required bit will be cleared.

REQUEST SENSE command to look at the CLN bit in the sense data. If the bit is set,

Monitoring tape use

Drives can report the actual amount of data that has been written to the tape, and the amount of available space on the tape. From this information, applications for Ultrium drives can be designed to calculate the percentage of tape used, and give the user feedback on the actual progress of the backup operation. This is a significant improvement over other technologies, such as DC6000 QIC products, that require the application to estimate what is going on.

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See “Tape Capacity Log Page” under the LOG SENSE command in Chapter 3 of The SCSI Interface, Volume 3 of the HP LTO Ultrium Technical Reference Manual for more information.

While the reliability of tape products and applications is getting better all the time, problems do still occur. There are some very simple techniques that could be incorporated by application developers to simplify the process that a user must go through to resolve problems.

For additional information, see “Exception handling” on page 77.

TapeAlert

The TapeAlert facility in HP Ultrium drives allows applications to help avoid trouble by prompting the user to take remedial action, or in some cases, through the application automatically performing remedial actions itself.

For example, if the drive is experiencing trouble writing, the software can prompt the user to clean the heads, or, if there are several drives or an autoloader, automatically clean the heads without involving the user.

See “Monitoring the condition of the drive and media” on page 78 for more details.

Diagnostic logs

SCSI tape drives report problems in response to a REQUEST SENSE command from the host. If the backup application stores this information in a log file, it becomes significantly easier to troubleshoot problems, because the data can be used to pinpoint what is wrong.

Displaying drive information

Troubleshooting can also be simplified by giving users the ability to look at the drive’s firmware revision, and information about the host bus adapter. This information can be found by executing an

INQUIRY command, and can then be displayed, or stored in a log file.

Drive tests

A basic read/write test should be included in a backup application to check the integrity of the hardware. This should also allow the user to scan the SCSI bus and to solve problems concerning the device setup and configuration.

Design goals for LTO backup applications

• Use large SCSI read/write transfer sizes (256 KB is recommended).

• Incorporate data compression control and report the compression ratios achieved.

• Consider where to store directory information depending on the nature of the application.

• Only use immediate

mode.

• Use Cartridge Memory information to measure tape quality before backing up starts.

• Use the TapeAlert log to prompt the user to take remedial action to avoid problems.

• Use “cleaning required” indicators in the software to either prompt the user or enable the library

to use a cleaning cartridge to clean the drive heads.

• Allow users to set custom cleaning schedules.

WRITE FILEMARK commands, but avoid using other commands in immediate

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• Use log files to store Inquiry and Sense Key/Error Code information about error conditions.

• Allow users to access drive firmware revision and HBA characteristic information

• Include the capability to download firmware.

• Incorporate simple diagnostic capabilities, such as Write/Read tests and SCSI device discovery.

• Incorporate online help.

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2 Configuration and initialization

This section covers the following topics:

• Operating System drivers

• Inquiry string recovery, finding information about the drive through the

• Additional LUN support, for operation with an autochanger device

• Fibre Channel support

Operating system drivers

Windows HP have a proprietary driver for Windows 2000 and Windows 2003. It is

intended that the driver is freely licensed to any software partner that requires it.

For the latest driver support for HP tape drives, please visit the following HP web site: http://www.hp.com/support/ultrium

NetWare HP has worked with Novell to provide driver support for HP’s Ultrium products. UNIX See the UNIX, Linux and OpenVMS Configuration Guide for details of how to

implement Ultrium support under the popular UNIX flavors.

Inquiry string recovery

HP Ultrium devices should not be recognized solely by the contents of their SCSI INQUIRY strings. In the past, hard-coded recognition of Inquiry strings has meant that software support for follow-on products from HP has been delayed when, to all intents and purposes, the new product was practically identical to the previous generation. For Ultrium, it is recommended that software applications ‘key off’ only the first eight bytes of the Product ID field—the text “Ultrium ”. Th e only use for the remainder of the bytes in this field is that they will be visible on-screen during the boot process of PC systems. As with HP’s DDS products, there will be very little difference between the first Ultrium drives and succeeding generations in terms of their basic SCSI characteristics; they will just store more data faster.

INQUIRY command

Standard INQUIRY Page Data SCSI SAS FC

Vendor ID (bytes 8–15) “HP ” “HP ” “HP ” Product ID (bytes 16–23) “Ultrium ” “Ultrium ” “Ultrium ” Product ID (bytes 24–31) “4-SCSI ” “4-SCSI ” “4-SCSI ” Product Revision Level (bytes 32–35) CRMV CRMV CRMV

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Product ID, first 8 bytes

“Ultrium ” This will be the same for all HP Ultrium products, regardless of generation or model.

Product ID, last 8 bytes

1st byte: Generation identifier:

“4” LTO 4 (1600 GB at 2:1 compression) 2nd byte “–” Hyphen separator (ASCII 2Dh) 3rd–6th bytes “SCSI” SCSI protocol, regardless of transport or interface type

Product Revision Level

1st byte Product codename ID:

“A” “B”

“H”

LTO 4 SAS full-height drive LTO 4 SCSI full-height drive LTO 4 FC full-height drive

2nd byte Release type:

“0”, “1”

“2”

“3”, ...

Development Formal release

Post-release 3rd byte Minor release level: “0”–“9”, then “A” –”Z” 4th byte Firmware variant:

“D”

“W”

Standard distribution firmware

Standard HP automation firmware

Example

If new drive families or variants support features that are not available in previous generation products, you can detect the existence of these features through the SCSI

SENSE

commands. Exact details will become available as new products are defined. There is no

need to limit driver or application connectivity to a single HP Ultrium product type.

To determine the drive technology family:

Examine only the first eight bytes of the Product ID field (the text “Ultrium ”).

To determine the Ultrium format generation:

Use one of the following two methods, of which the second is preferred:

• Examine the character in byte 9. A “4” indicates format LTO 4 (1600 GB capacity at 2:1

compression) and so on.

• Preferred method: Use the SCSI REPORT DENSITY SUPPORT command.

For an LTO 4 product with LTO Ultrium 4 media, the following will be returned:

Primary Density Code: 46h Assigning Organization: LTO-CVE Linear Tape Open Compliance and Verification Entity Density Name: U-416 16 track

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MODE SENSE and LOG

Since LTO 4 drives cannot write to Ultrium-2 media, the WRTOK bit will be clear for this media type.

Support for additional LUN

Enabling additional LUN support

When enabled by an internally-connected autochanger device, an extra Logical Unit Number (LUN) will be available at the target’s SCSI ID. This allows the attached autochanger device to be addressed via the tape drive. See ”Automation interface” on page 35. For ADI Bridging usage, the automation LUN will usually be LUN1.

No other LUNs are available on the drive, although HP is looking to provide new functionality through the use of additional LUNs in future products.

Supporting additional LUNs

When working with a library vendor who is incorporating HP Ultrium drives in products, software developers should liaise directly with the vendor about the functionality of the hardware available through the ADI or ACI.

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Configuration and initialization18

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3Use of tapes

HP Ultrium user documentation and “Cartridges”, Chapter 9 of the Hardware Integration Guide, Volume 1 of the HP LTO Ultrium Technical Reference Manual, also contain information on cartridges.

Timing considerations are discussed in “Time-out values” on page 28.

LTO cartridge memory

NOTE: “Cartridge Memory” is the Ultrium version of the more general term “Media Auxiliary

Memory” or MAM, covering all media types.

Cartridge Memory has been added to the LTO cartridge for the following reasons:

• It speeds up load and unload times by removing the need to read system areas.

• It speeds up movement around tape by storing the tape directory (physical to logical mapping).

• It increases tape reliability because fewer tape passes are needed.

• It stores diagnostic and log information for tracking purposes.

Most of these uses are invisible to applications and handled internally by the drive. There is potential for applications to use the “Application Specific Data” area. This is being investigated.

For more details, see “Using Cartridge Memory” in “Using Special Features in Libraries”, Chapter 2 of the Hardware Integration Guide, Volume 1 of the HP LTO Ultrium Technical Reference Manual.

Identifying tape cartridge types

Using Cartridge Memory attributes

To identify the type of cartridge in the drive, read the Medium Type attribute in Cartridge Memory:

Attribute ID 0408h 00h

Using MODE SENSE

Examine the Medium Type field in the Mode Parameter header of the MODE SENSE command (byte 1 in the 6-byte version, byte 2 in the 10-byte version):

Medium Type 00h

01h 80h

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Read/write (normal) data cartridge

01h

Cleaning cartridge

80h

WORM cartridge

Read/write (normal) data cartridge WORM cartridge SCSI and SAS only: CD (the drive is in CD-ROM mode)

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Tape status and capacity

Following autoload or a LOAD command, the software can determine the state of the tape and its capacity from the Cartridge Memory and the Tape Capacity Log pages retrieved through the

SENSE

command. The information can also be invoked as a console operation at any time to find

the status and condition of the media.

Tape capacity figures can be used for two purposes:

• To give an application or user an indication of whether the tape has enough capacity for a

proposed backup. When using data compression, however, this is of little value, since the compression factor cannot be predicted accurately.

• Periodically during a backup to give an approximation of the amount of tape left.

CAUTION: An application should not use the capacity reported in the Tape Capacity log to fix the

backup size. This will result in permanent capacity truncation that could represent a significant percentage of the available capacity.

Finding the remaining capacity

Examine the Tape Capacity Log to estimate the effective remaining capacity of the tape (data-compression factors are not considered).

Interpreting Log Sense data

The following points affect the values returned in the data:

LOG

Units Capacities are given in megabytes (1,048,576 bytes) of user data and assume no

compression.

General • If data compression is used, the capacities are specified as though the drive is in

pass-through mode. The data compression factor is not considered.

• Regions of tape used by the system, such as EOD areas, are not included in

capacities specified. In other words, values are conservative.

• An allowance for read-after-write retries is made.

Maximum Capacity

Remaining Capacity

Use of tapes20

Maximum capacity values are only valid when the tape has completed a load sequence. If an immediate mode information until the tape has been successfully loaded and tape motion has ceased.

The remaining capacity value is the amount of tape remaining calculated from EOD. Remaining capacity values are only valid after the successful completion of the

following commands in non-immediate mode:

LOAD LOCATE MODE SELECT READ REWIND SPACE VERIFY WRITE WRITE FILEMARKS

The values after any subsequent command cannot be relied on unless the command is a sense type that does not cause any tape motion.

LOAD is made, LOAD SENSE will not return valid

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Capacity calculations are based on estimates; reported values can be subject to error in two ways:

• Random errors caused by tolerances in tape length, hub diameter, and so on.

• Systematic errors caused by ignoring system areas, and so on. They ensure the calculated

capacity is actually available to the user. It is usually possible to write considerably more data than the calculated capacity.

Using the SET CAPACITY command

You can modify the capacity of a tape by changing the logical length of the tape through the SET CAPACITY command. The primary use envisaged is for testing purposes, although it may also be used in other circumstances where a shortened tape may be beneficial.

NOTE: All data currently on the tape will be lost following successful execution of this command.

The command is only accepted when the media is positioned at Beginning of Media (BOM).

With WORM cartridges, the command is only accepted and executed if the cartridge has not been initialized, that is, it has never been written to. Otherwise the cartridge is rejected with

CONDITION

attempted). TapeAlert flags 3Ch (WORM media—overwrite attempted) and 09h (write-protect) are set.

Command descriptor block

, sense key of Data Protect and additional sense of 300Ch (WORM media—overwrite

CHECK

76543210 0 Operation Code (0Bh) 1 Reserved (0) Immed 2 Reserved (0) 3 (MSB) 4 (LSB)

Capacity Proportion Value

5 Control

CDB fields

Immed 0 Status will not be returned until the

1 Status will be returned as soon as the CDB has been parsed.

Capacity Proportion Value

The portion of the total volume capacity to be made available for use. The value is the numerator of a fraction with a denominator of 65,535. The resulting

total volume capacity capacity proportion value×

available capacity will be .

------------------------------------------------------------------------------------------------------------------------------- -

Note that the LTO-4 format enforces a minimum tape length. A value that would result in a tape length below this minimum will be silently rounded up to the minimum permitted length.

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SET CAPACITY operation has completed.

65535

The following table gives the minimum acceptable Capacity Proportion Values and the approximate capacity they will give:

Cartridge Min. capacity proportion value Resultant approx. min. capacity Max. capacity

Ultrium 2 Ultrium 3 Ultrium 4

NOTE: Capacities are approximate and can be affected by defects that reduce the actual capacity

of the tape. Other factors, such as compression and block packing, may also affect capacity.

WORM media

HP Ultrium-3 WORM (Write Once—Read Many) data cartridges are two-tone grey/yellow to distinguish them from RW media. They have a unique Cartridge Type stored in the Cartridge Memory, so that they will be rejected by non-WORM compatible drives. For automation configurations with auto-eject disabled, the cartridge will not be physically ejected from the drive but held at the “ready eject” position.

The write-protection tab behaves as on Read/Write (RW) cartridges.

How WORM media works

Drives use the EOPD (End of Protected Data) value to control the use of WORM tapes.

1605h 17.2 GB 200 GB

151Ah 33 GB 400 GB

1055h 51 GB 800 GB

EOPD is a logical position on tape that is automatically calculated based on the End of Data (EOD) value read from the Cartridge Memory (CM) when the cartridge is loaded into the drive. The EOD value is an “intrinsic” code stored and protected in the Cartridge Memory of each WORM cartridge, and updated after each write session. The EOPD indicates that data between BOM and this position cannot be overwritten.

The EOPD value is held within the drive’s memory. It is updated automatically and continuously as each block of data (typically 64 or 128 KB) is written to tape, so the EOPD value indicates a logical position immediately after the last block of data written to tape.

When the cartridge is unloaded, the drive updates the EOD value in CM to reflect the end of successfully written data on the cartridge, and clears the EOPD value stored within the drive. Any future writes to the cartridge will occur after the location of the EOD, which will become the initial location for EOPD during the next write operation.

Changes to SCSI commands

New additional sense codes and TapeAlert flags

ASC/Qs:

• 300Ch (WORM medium—overwrite attempted)

• 300Dh (WORM Medium—integrity check failed)

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TapeAlert flags:

• 3Bh (WORM medium—integrity check failed)

• 3Ch (WORM medium—overwrite attempted)

Error Usage page

For WORM cartridges, the Wrap Number fields in the Error Usage page are replaced by an Error Code field. This contains the ASC/Q value reported to the host when the associated error was detected.

Only appended writes accepted

If a WORM cartridge is placed in a WORM-compatible drive, the drive will accept write commands (records, filemarks) only if the current logical position is beyond the position identified by the EOPD value. If a write command is received by the drive when the logical position is before the EOPD value, the command will be rejected and Protect and additional sense of 300Ch (WORM medium—overwrite attempted). The TapeAlert flags 3Ch (WORM medium—overwrite attempted) and 09h (write-protect) are set.

CHECK CONDITION returned with sense key of Data

ERASE commands rejected

ERASE commands (short or long) to a drive containing a WORM cartridge will not overwrite or erase user data on tape. Any tape is rejected and sense of 300Ch (WORM medium - overwrite attempted). The TapeAlert flags 3Ch (WORM medium—overwrite attempted) and 09h (write-protect) are set.

CHECK CONDITION returned with sense key of Data Protect and additional

ERASE command that would result in user data being over-written on

SET CAPACITY command

The SET CAPACITY command will only be accepted and executed if the WORM cartridge has not been initialized, that is, it has never been written to.

If a

SET CAPACITY command is received by the drive when the cartridge has been initialized, it is

rejected and 300Ch (WORM medium—overwrite attempted). The TapeAlert flags 3Ch (WORM medium—overwrite attempted) and 09h (write-protect) are set.

CHECK CONDITION returned with sense key of Data Protect and additional sense of

Re-writing media labels

If there is no user data on the tape, the media label can be rewritten. The label contains software application-related information such as a unique identification code and does not contain user data.

Writing is allowed when the current logical position is at BOT and:

• there are only filemarks between this position and EOD, or

• there are only 1 or 2 sequential records followed by any number of filemarks, but no further

records, between this position and EOD.

Allow overwrite of last filemarks before the EOD data set

At the end of a backup or archive session, many software applications write two filemarks to tape immediately before the EOD data set is written. These filemarks are logical markers that enable the

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application to locate the tape in preparation for subsequent writing or reading operations. At the start of an appending archive or backup session, it is common for the application to locate the tape to a logical position immediately preceding the second filemark and to overwrite the second filemark during the data appending session.

Writes are allowed:

• when the current logical position is at EOD. This means that the drive must have read the EOD

from tape before attempting to overwrite it.

• when there are only filemarks between the current logical position and EOD, and at least one

filemark immediately before the current logical position.

Using CM to check tape integrity

Drives that support WORM cartridges check that the anti-tampering measures have not been violated before and during media access operations. If a violation is detected, for example, if the content of the CM does not match the content of the tape, the cartridge is treated as read-only, and Tape Alert flag 3Bh (WORM medium—integrity check failed) is set.

HP strongly recommends that software applications check for the presence of TapeAlert flag 3Bh after a tape load and periodically during operation. If the flag is set, the software should alert the operator and log the incident for audit.

Hosts can use the WTRE bit on the Device Configuration mode page (bit 6, byte 15 of mode page 10h) to control the behavior of the drive when reading WORM media whose WORM integrity is in doubt and which may have been tampered with. See details of the mode page in Chapter 4 in SCSI Interface, volume 4 of the HP LTO Ultrium Technical Reference Manual for more information.

Behavior with a missing or inconsistent EOD value

A missing EOD value or one in which the value on tape differs from that in CM can be caused by:

• CM corruption

• deliberate, malicious alteration of the EOD value in the CM

• an interruption of the drive power supply while writing data.

If the CM indicates that the EOD is not valid (for example, if the drive has powered down during a write), TapeAlert flag 04h (Media) will be set on cartridge load.

The drive behaves as for a RW cartridge with no EOD data set, except that any attempt to overwrite data will be rejected with C 2700h (write-protected). Tape Alert flag 09h (Write-Protect) is set.

HECK CONDITION, a sense key of Data Protect and additional sense of

Unique media identifier

For added security, HP strongly recommends that applications read and track cartridge manufacturer and serial number values from the Cartridge Memory using MAM access commands:

• Attribute ID 0x0400: Cartridge manufacturer ID

• Attribute ID 0x0401: Cartridge serial number

Both values should be read and concatenated to ensure that the number is unique.

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Barcode support

Ultrium barcode support is required for WORM media so that the application and tape library can distinguish WORM media from normal RW media or cleaning cartridges.

HP recommends the use of the following barcode formats for Ultrium media:

123456L2 LTO Ultrium 2 123456L3 LTO Ultrium 3 123456L4 LTO Ultrium 4

::

123456LT LTO Ultrium 3 – WORM

123456LU LTO Ultrium 4 – WORM

::

Responding to Cartridge Memory data

NOTE: Software should use the TapeAlert log in preference to the Cartridge Memory to detect

conditions which require the user or host to take preventative action. See “Monitoring the condition

of the drive and media” on page 78.

These guidelines indicate how host applications should make use of the data contained in the Cartridge Memory during normal operation (that is, when tapes are not permanently write-protected, not constantly re-formatted).

The console messages triggered by these criteria should clearly indicate a course of action to the end-user, such as the following:

1. Clean the tape heads using a cleaning cartridge.

2. Insert a new tape cartridge.

3. Archive the data.

Load count

NOTE: This only applies when non-write-protected cartridges are used.

The load count is the number of times the cartridge has been loaded into a drive and accessed.

Hewlett-Packard recommends a maximum use for a tape of 20,000 passes over any particular area of the tape. This conservative estimate is also influenced by the quality of the application and the driver software in being able to maintain streaming, thereby preventing repositioning over the same area of tape, without data being transferred.

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RWW retry counts

Data is read immediately after being written to tape to establish that it has been written correctly. Increases in RWW retries can be due to four factors:

• Deterioration in the media

• Dirty heads

• Drive malfunction

• The operating environment

Corrective action

The recommended criteria for corrective action are as follows:

RWW Retries > 5% Total data sets written

When using tapes without write-protection, use the Total count.

The corrective action should be as follows:

1. Use another tape and, for a write operation, try repeating the write. For a read operation, try

reading data from the tape.

2. See whether the current RWW value is within the recommended limit.

3. If the values are now within the limit, you can assume that the original tape is nearing the end of

its useful life. Proceed as follows:

• For a write operation, discard the tape and use a new one.

• For a read operation, transfer the data to a new tape.

4. If the value is still outside the limit, clean the tape heads with a cleaning cartridge and try

repeating the operation with the original tape.

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4 Factors affecting performance

This chapter contains techniques and information to help you design software applications so that they use the tape drive’s potential as efficiently as possible.

• Ways of optimizing performance:

• Ensuring the recommended minimum transfer sizes page 27

• Identifying the media type page 28

• Using Cartridge Memory instead of tape headers page 28

• Using the Performance Log page to diagnose problems page 28

• Time-out values to help you tune timings in backup applications page 28

• Log pages—recommended support page 29

• Factors affecting performance, relating separately to the host, drive and format page 29

Ways of optimizing performance

HP’s Ultrium drives are high-performance products. Application software may require significant enhancement in order to capitalize on this speed. There are a number of areas to look at and these are discussed below.

Further details can also be found in the “How to optimize the performance of hp ultrium tape drives” white paper.

Detecting the drive’s speed

Applications should not key off Inquiry strings in order to tell the difference between different speed drives. It is better to use the Performance Log page see under the 4, “Commands”, of SCSI Interface, Volume 3 of the HP LTO Ultrium Technical Reference Manual.

In the Performance Log page (34h), parameter 04h (Native data rate) gives the native data rate of the drive in units of 100 KB/s. LTO 4 drives give the value 04B0h, indicating 120 MB/s with Ultrium 4 media or no cartridge loaded. If a previous generation cartridge is loaded, the value will be lower.

Ensuring the recommended minimum transfer sizes

Use the Data Compression Log page. HP cannot diagnose performance issues without accurate reporting of the current compression or the average compressibility over a backup session. Make sure that you report the log page.

Regarding HP’s One-Button Disaster Recovery (OBDR) feature (see “One-Button Disaster Recovery

(OBDR)” on page 89), it is important to note that in some situations the SCSI block size may have to

be fixed for a given tape for format reasons. This means that if the host writes 2 KB blocks to support OBDR, it may have to continue to write 2 KB blocks for the rest of the tape; it depends on the format compatibility required by the overall system. However as HP Ultrium drives are insensitive to

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LOG SENSE command in Chapter

absolute block size, performance should not suffer, but do ensure that the transfer size is at least

256 KB.

Maximum block size

The READ BLOCK LIMITS command indicates that block sizes and variable length transfer sizes are supported for values between 1 byte and 16,777,215 bytes.

Media type identification

HP recommends that you use the REPORT DENSITY SUPPORT command (with the Media bit enabled) to identify the type of media loaded in the drive.

Using Cartridge Memory instead of tape headers

For optimum performance, it is also important that the host writes application tape header information to the Cartridge Memory (see “Cartridge Memory (LTO-CM)” on page 35) rather than to the actual tape. This allows cartridges to load and unload quickly and prevents excessive media wear at the beginning of the tape. As the access method to Cartridge Memory data is an open standard, it also permits other software systems to identify alien media positively in shared storage environments.

Using the Performance Log page for diagnosing problems

The Performance Log page (34h) contains data that should allow application software to monitor the data-rate being sent to the drive dynamically. For details, see the Volume 3, SCSI Interface, of the HP LTO Ultrium Technical Reference Manual.

LOG SENSE command in

Time-out values

SCSI Command Recommended Time-Out Value

Load 10 minutes Unload 10 minutes Rewind (full tape length) 10 minutes Space/Locate/CD-ROM Read (10) 20 minutes Erase (long) 5 hours Erase (short) 5 minutes Write/Write Filemarks 5 minutes Read 20 minutes Read/Write Attribute (MAM), with 1 KB of attribute data 1 minute Non-tape movement (such as TEST UNIT READY, INQUIRY) 1 minute

Notes:

• These values are for a single SCSI command in non-Immediate mode. As most commands will

be sent in Immediate mode, status will be received by the host typically within 20 ms. In such cases, the time-out given indicates when the drive will have completed the operation and be ready for the next tape movement command.

Factors affecting performance28

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• All of these values may be subject to change.

• There is no retension facility.

Recommended support of log pages

Some of the media-related data items on the log pages are duplicates of data that is available through the specification. We recommend that you use MAM commands as the primary source for such data, because this access method is portable to tape drives from other vendors, that is, the data is not in a vendor-unique format.

In the long term, HP intends to expose all tape usage and drive hardware usage information via the industry-standard MAM-format commands, so it is wise to start to implement this approach now.

READ ATTRIBUTES command using the Media Auxiliary Memory (MAM) access

For full details of the Ultrium log pages, see the of SCSI Interface, Volume 3 of the HP LTO Ultrium Technical Reference Manual.

Factors affecting performance

Further details on improving performance can be found in the “How to optimize the performance of hp ultrium tape drives” white paper.

Host-related factors

Performance Factor Detail

Host SCSI performance The execution of each SCSI command involves a number of bus

phases, of which the data phase is only one. The key phases are as follows:

• Intra-command bus-free time

• Arbitration and selection

• Message out

• Command

Host Burst Rate During the data phase of each SCSI command, data is transferred to

or from the drive at the host’s burst rate. If the host’s burst rate is slow, then it takes longer to transfer the data. Extra time during this phase is simply added to the total command time, and so it can affect the overall performance.

Even if the burst rate is much faster than that required to maintain streaming, the total command time may prevent the commands from being issued fast enough.

LOG SENSE command in Chapter 4, “Commands”,

HP LTO Ultrium 4 drives technical reference manual, volume 2: software integration 29

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HP LTO 4 SAS, LTO 4 SCSI, LTO 4 FC User Manual

Contents

Related documents

Documents specific to HP Ultrium drives

Documentation map

Installation and configuration

Operation

Cartridges

Interface

Maintenance and troubleshooting

Dealing with errors

LTO Ultrium features

General documents and standardization

1 Designing backup applications

Optimizing performance

Large data transfer size

Data compression control

Non-immediate commands

Managing the use of tapes

Information in Cartridge Memory

Cleaning tape heads

Monitoring tape use

TapeAlert

Diagnostic logs

Displaying drive information

Drive tests

Design goals for LTO backup applications

2 Configuration and initialization

Operating system drivers

Inquiry string recovery

Support for additional LUN

Enabling additional LUN support

Supporting additional LUNs

LTO cartridge memory

Identifying tape cartridge types

Tape status and capacity

Finding the remaining capacity

Interpreting Log Sense data

Using the SET CAPACITY command

WORM media

How WORM media works

Changes to SCSI commands

Re-writing media labels

Allow overwrite of last filemarks before the EOD data set

Using CM to check tape integrity

Behavior with a missing or inconsistent EOD value

Unique media identifier

Barcode support

Responding to Cartridge Memory data

Load count

RWW retry counts

4 Factors affecting performance

Ways of optimizing performance

Detecting the drive’s speed

Ensuring the recommended minimum transfer sizes

Media type identification

Using Cartridge Memory instead of tape headers

Using the Performance Log page for diagnosing problems

Time-out values

Recommended support of log pages

Factors affecting performance

Host-related factors