IBM Support

Potential data corruption SAS disk write cache is enabled - IBM System x

Troubleshooting


Problem

When disk write cache is enabled on any of the listed Hard Drives, data corruption can occur. The system will not incur any issue. The Operating System (OS) will likely not indicate any event. Data corruption occurs without the users awareness when the active disks write cache is enabled and the disk performs a Read Look Ahead (RLA), which is prematurely ended. Data corruption can occur when cached write data which has not been committed to disk is invalidated by a completed disk read operation and thenread at a later time.

Resolving The Problem

Source

RETAIN tip: H197710

Symptom

When disk write cache is enabled on any of the listed Hard Drives, data corruption can occur.

The system will not incur any issue. The Operating System (OS) will likely not indicate any event. Data corruption occurs without the users awareness when the active disks write cache is enabled and the disk performs a Read Look Ahead (RLA), which is prematurely ended. Data corruption can occur when cached write data which has not been committed to disk is invalidated by a completed disk read operation and then read at a later time.

Affected configurations

The system is configured with one or more of the following IBM Options:

  • 1 TB 7200 NL SAS 3.5-inch HS HDD, Option 42D0547, any replacement part number
  • 146 GB 10,000 RPM 2.5-inch NHS SAS SFF HDD, Option 42D0421, any replacement part number
  • 146 GB 10,000 RPM 3.5-inch SAS Hot-Swap HDD, Option 40K1040, any replacement part number
  • 146 GB 15,000 RPM 3.5-inch SAS Hot-Swap HDD, Option 40K1044, any replacement part number
  • 146 GB 15,000 RPM 6 Gbps 2.5-inch SAS SFF Slim Hot-Swap HDD, Option 42D0677, any replacement part number
  • 146 GB 15,000 RPM 6 Gbps SAS 2.5-inch SFF Slim Hot-Swap SED, Option 44W2294, any replacement part number
  • 146 GB SAS HDD, Option 26K5710, any replacement part number
  • 300 GB 10,000 RPM 3.5-inch SAS Hot-Swap HDD, Option 40K1041, any replacement part number
  • 300 GB 10,000 RPM 6 Gbps 2.5-inch SAS SFF Slim Hot-Swap HDD, Option 42D0637, any replacement part number
  • 300 GB 10,000 RPM 6 Gbps SAS 2.5-inch SFF slim Hot-Swap SED, Option 44W2264, any replacement part number
  • 300 GB 15,000 RPM 3.5-inch SAS Hot Swap HDD, Option 43X0802, any replacement part number
  • 750 GB 7200 NL SAS HS 3.5-inch HDD, Option 42D0546, any replacement part number

This tip is not system specific.
This tip is not software specific.

Solution

This behavior will be corrected in a future release of the Hard Disk Update Program.

The target date for this release is scheduled for third quarter 2010.

The file is or will be available by selecting the appropriate Product Group, Product name, Product machine type, and Operating system on IBM Support's Fix Central web page, at the following URL:


Workaround

Disable disk write cache.

Additional information

While performing extended disk test exercises, a latent firmware issue was discovered. Although rare, there is a potential for data corruption with hard disk write cache enabled.

This potential issue results from insufficient overlap checking being performed when the write command is received. If a RLA is allowed to fill the entire cache segment, chances are it will overwrite the complete range with new cached data eliminating the overlapping condition. However, the potential for data corruption occurs when a RLA does not fill the entire cache segment and stale data is read from the uncleared portion.

A firmware Fix was implemented to increase stream overlap range checking on incoming Write commands. In such cases, streaming will now be temporarily stopped to handle the new write command, where as before it could have continued the RLA (reads beyond a given read command range of LBAs as a potential cache hit) operation.

The engineering recommendation is to disable disk write cache and update hard disk firmware during the first available scheduled maintenance.

 

Document Location

Worldwide


Operating System

System x:Operating system independent / None


Applicable countries and regions

  • Worldwide
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Document Information

More support for:
System x->System x3800

Document number:
857902

Modified date:
30 January 2019

UID

ibm1MIGR-5086048

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