FS System: What do Hosts Report when Read Before Write Access Performed

Asset ID:	1-72-2140141.1
Update Date:	2018-01-03
Keywords:

Solution Type Problem Resolution Sure

Solution 2140141.1 : FS System: What do Hosts Report when Read Before Write Access Performed

Applies to:

Oracle FS1-2 Flash Storage System - Version All Versions and later
Information in this document applies to any platform.

Symptoms

When a host performs read I/O to volume blocks that have not been written to AND 'reference tag' checking is enabled on that volume, the following messages may be recorded on the host.

Solaris OS (with Qlogic HBA 'qlc' driver and 'extended-logging' (debug) enabled.)

May 20 07:32:59 hostname qlc: [ID 742775 kern.info] 1497=>QEL qlc(0,0,0):: qlc_24xx_status_error, transport error - underrun & invalid resid
May 20 07:32:59 hostname qlc: [ID 434913 kern.info] 1498=>QEL qlc(0,0,0):: qlc_24xx_status_error, ssh=0h, ssl=28h
May 20 07:32:59 hostname qlc: [ID 325030 kern.info] 1499=>QEL qlc(0,0,0):: qlc_24xx_status_error, transport error - underrun & invalid resid
May 20 07:32:59 hostname qlc: [ID 625491 kern.info] 1500=>QEL qlc(0,0,0):: qlc_24xx_status_error, ssh=0h, ssl=28h

On the FS1-2, an event will also be recorded similar to the following example:

Event Properties

Event: SLUN Read Before Write
Category: System
Time Occurred: Wed May 25 14:31:32 AEST 2016
User: (system)
Affected Item: /volumename

Description:

A client read from an area of an SLUN that has never had data written to it.

SanEventSlunReadBeforeWrite.slunGuid: 6000B08414B30303137343839390070D

Cause

The Oracle FS1-2 storage system performs integrity checks which include adding a reference tag to data when it is written and subsequently checked when later reread. As a result of not having previously written to a LUN block prior to reading from it, that check will fail and notification passed to the host.

The messages observed are the consequence of this action. The I/O is redriven by the host in this instance without issue.

Solution

The Solaris 'QEL' messages are only observed if the Qlogic HBA driver has debug enabled. The messages should not be observed during normal system use and are information debug in nature, not an error thus should be ignored.

The FS1-2 can optionally disable this feature or automatically disable the feature.

For more information on Reference tag checking please refer to Oracle Flash Storage System Administrator's Guide and Document 1955116.1 FS System: When To Use "Use as Boot LUN" and "Disable Reference Tag Checking" Options For FS1-2 LUNs

References

<NOTE:1955116.1> - FS System: When To Use "Use as Boot LUN" and "Disable Reference Tag Checking" Options For FS1-2 LUNs

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