Tape devices do not support concurrent access

Asset ID:	1-71-1011221.1
Update Date:	2011-02-02
Keywords:

Solution Type Technical Instruction Sure

Solution 1011221.1 : Tape devices do not support concurrent access

Applies to:

Sun Storage L100 Tape Library
Sun Storage L25 Tape Library
Sun Management Center - Version: 3.0 and later    [Release: 3.0 and later]
Solstice Backup (SBU) Software - Version: 4.2 and later    [Release: 4.0 and later]
Veritas NetBackup (NBU) Software - Version: 3.0 and later    [Release: 3.0 and later]
All Platforms
Checked for relevance on 2-Feb-2011.

Goal

The purpose of this document is to highlight that tape devices are single-access devices and may cause problem when accessed concurrently.

Solution

Steps to Follow

Tape devices are single-access devices. This means that there can only be one access to the tape device at any time.

This limitation is usually not an issue for tape devices on SCSI bus where there is usually only one initiator on the SCSI bus. However, since the introduction of SAN technology, it has become very common to have multiple hosts/applications accessing SAN attached tape devices. As a result, many tape related bugs has been filed. Many infdocs/SRDBs were also written to workaround this tape device limitation. Below is a small sample of the list of bugs and infodocs/SRDBs.

bugid   synopsis
------- -------------------------------------------------------------------
2100751 Tape I/O fails after Link Reset
5096649 SunMC config-reader lacks user interface to disable tape monitoring
4665844 srs2.1.1/Config-Reader causes SAN-attached tape devices to interrupt backups.
5056082 Excessive CPU usage while gathering tape drive information
6475248 SunMC3.6.1: config reader modules for tape devices disturbs NetBackup
4800401 Config Reader causes tapes to rewind on 280R, V480 and V880.
------- -------------------------------------------------------------------

infodoc
/SRDB   Synopsis
------- -------------------------------------------------------------------
78514   Tips on increasing reliability of SAN based backup - FCP2 error recovery protocol.
------- -------------------------------------------------------------------

What is the fix?

Until Tape devices are capable of supporting concurrent access or standards are written for concurrent access to shared tape devices, the only fix now is to ensure single-access to tape devices?

Below is an example on how single access to tape device is implemented in an environment where a tape device is concurrently accessed by SunMC and SBU.

Example:

 When using SBU for backup and SunMC to monitor systems, tape backup
would fail when SunMC tries to probe the tape drive while SBU backup is
in progress.

 The fix is to turn off monitoring of tape devices by SunMC as follows:

 # /opt/SUNWsymon/sbin/es-setup
...
The Domain Config Reader for Sun Fire 15K/12K systems will collect configuration
and status information for your tape drives at regular polling intervals. This
can be disruptive to tape drive controllers that do not allow concurrent access.

 Would you like to disable this feature? [y|n|q] y

Product
S0YAA4O Internal ID use only.

Internal Comments

The following are list of Sun internal-pm;u bugids and srdbs.

bugid/

 srdb    Synopsis

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

 4483228 config reader should use sd,err (iostat -E) kstat for the tape device

 81842   Path to FC tape drive intermittently goes offline for exactly 10 minutes

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

SBU, NetBackup, EBU, NBU, netback, up, backup, sso, tape, SAN, SunMC, Sun MC, Management Center, Management Centre, Symon, L25, L100, Config-Reader, ConfigReader, Config Reader
Previously Published As 88024

Change History
Date: 2006-12-18
User Name: 95826
Action: Approved
Comment: - checked audience of listed documents : ok
- replaced 'customer using ' with 'when using'.
- verified metadata
- review date ok : 2007-12-11
- checked for TM - none added
butor-standards.html
- checked audience : contract
Publishing
Version: 4
Date: 2006-12-18
User Name: 95826
Action: Accept
Comment:
Version: 0
Date: 2006-12-17
User Name: 35723
Action: Approved
Comment: Changed reference to BugID (4483228) and InfoDocs/SRDBs (81842) to internal only area.
Version: 0
Date: 2006-12-14
User Name: 97961
Action: Rejected
Comment: As this article is tagged for "Contract" audience, it is against our publish standard to make reference in the main body to a BugID (4483228) and InfoDocs/SRDBs (81842) that are tagged for "Internal" audience.

References to "Internal" resources should only be made in the "Internal Only" section of the document.

Please make the necessary amendments.
Version: 0
Date: 2006-12-14
User Name: 97961
Action: Accept
Comment:
Version: 0
Date: 2006-12-14
User Name: 35790
Action: Approved
Comment: The document looks good. Please review and publish.

- Bala.
Version: 0
Date: 2006-12-11
User Name: 35723
Action: Approved
Comment: This document highlight the fact that tape devices does not support concurrent access and that many tape backup failures are results of such limitation. The document has references to bugids, infodocs and SRDBs to make it easier for support engineers to related the problem seen by them to this limitation. In addition, this will also be a good document to share with customer to educate them on the current limitation of tape devices.
Version: 0
Date: 2006-12-11
User Name: 35723
Action: Created
Comment:
Version: 0

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