There are three symptoms found in firmware builds 11844, and below, regarding hard disk drive write-cache modes and how they may change unexpectedly: 1. When using F6 to reset the controllers default settings within the Adaptec Configuration Utility (ACU), CTRL-A, the default hard disk drive write-cache policy changes from the previous default of write-through (disabled) to write-back (enabled). 2. The user cannot change the write-cache policy of an individual drive within the ACU from write-back (enabled) to write-through (disabled). 3. A hard disk drives write-cache policy changes from write-through (disabled) to write-back (enabled) after the drive fails and is then replaced. Messages may appear in the operating system stating that the hard disk drive write-cache policy is enabled and that the data may be at risk. There is the potential of losing data if an unexpected power outage occurs, while using hard disk drives configured with the write-cache policy enabled or set to on.
Source
RETAIN tip: H19671
Symptom
There are three symptoms found in firmware builds 11844, and below, regarding hard disk drive write-cache modes and how they may change unexpectedly:
- When using F6 to reset the controllers default settings within the Adaptec Configuration Utility (ACU), CTRL-A, the default hard disk drive write-cache policy changes from the previous default of write-through (disabled) to write-back (enabled).
- The user cannot change the write-cache policy of an individual drive within the ACU from write-back (enabled) to write-through (disabled).
- A hard disk drives write-cache policy changes from write-through (disabled) to write-back (enabled) after the drive fails and is then replaced.
Messages may appear in the operating system stating that the hard disk drive write-cache policy is enabled and that the data may be at risk.
There is the potential of losing data if an unexpected power outage occurs, while using hard disk drives configured with the write-cache policy enabled or set to on.
Affected configurations
This tip is not hardware specific.
The system is configured with one or more of the following IBM Options:
- ServeRAID-8i Controller, Option 13N2227
- ServeRAID-8k SAS Controller, Option 25R8064
- ServeRAID-8k-l SAS Controller, Option 39R8729
- ServeRAID-8s SAS PCIe Controller, Option 39R8765
This tip is not software specific.
Solution
Download and apply the IBM ServeRAID firmware update build 15407, or higher. The new ServeRAID firmware changes the user interface for setting hard disk drive cache modes. Individual drive cache modes are no longer changed on a per-drive basis as with previous levels of code. The new settings establish a controller wide settings for SAS and SATA hard drives. Any SAS or SATA drive installed into the controller will be made to conform to this user configurable option. These setting can be found within the new ACU interface:
Perform the following when prompted during the ServeRAID-8x POST banner:
- Press CTRL-A to enter into the ACU.
- Select "Serial Selection Utility".
- Select "Controller Configuration".
-
Change the drive write -cache policy to one of the following options:
| |
SATA=ON, SAS=OFF (default setting)
SATA=ON, SAS=ON
SATA=OFF, SAS=ON
SATA=OFF, SAS=OFF |
- Save settings and exit.
The file is available from the Servers - ServeRAID Software Matrix.
Workaround
If upgrading to the latest code is not an option at this time, the hard disk drive write-cache can be disabled manually with the following steps: Perform the following when prompted during the ServeRAID-8x POST banner:
- Press CTRL-A to enter into the ACU.
- Select "Serial Selection Utility".
- Select "Controller Configuration".
- Change the drive write-cache setting to Disable.
- Save settings and exit.
Additional information
Managing hard disk write-cache policies on the ServeRAID-8 series controllers was improved to make this a global controller setting so all hard drives attached to the subsystem will conform to a common-cache policy. The write-cache policy can be set differently for SAS and SATA drives.
If the the hard drive write-cache mode is set to "on" or "enabled", a moderate performance gain can be expected at the risk of losing data should an unexpected power loss condition occur within the subsystem. Data loss can occur because the ServeRAID controller cannot manage outstanding write operations owned by the individual hard disk drive that may not be committed to the drive media. The battery backed memory cache on the ServeRAID controller can only protect the write operation at a logical drive level.
For this reason, IBM suggests that the hard drive write-cache policy be set to "off" or "disabled". Turning the write-cache off on all drive ensures the lowest risk to data loss in the event of an unexpected power outage.
System x Hardware Options:All operating systems listed
System x:Operating system independent / None
Older System x:Operating system independent / None
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