AMCC 3WARE 720-0138-00 - Manual (Page 57)

Setting Unit Policies
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• FUA (Force Unit Access) . FUA commands are a way that the RAID
controller or a program (such as a database program) can ensure that data
is actually written to the disk drive media, and is not stored in cache.
When a write command is followed with a FUA command, then the disk
drive will only issue “command complete” to the controller once the data
is written to media. When performance is considered more important than
protection, it may be desirable to ignore FUA commands.
The Protection and Balanced profiles honor FUA commands; the
Performance profile ignores them.
• Write Journaling . Write journaling tracks the writing of data to disk and
preserves a copy of data that has not yet been written to the disk media.
Following a power failure or in the event of accidental drive removal and
reinsertion, the firmware can recover the unit without data loss. All
pending writes sitting in the controller cache are replayed after power is
restored or the drive is reinserted and are flushed from the controller to
the drive.
Using write journaling helps protect your data, however it can have an
impact on performance.
The Protection profile enables write journaling; the Performance and
Balanced Profile disables it.
• Write cache disabled on degrade . In the event that a unit degrades, the
use of write cache can be disabled until the unit is rebuilt. Once the unit is
rebuilt, you must enable the write cache manually. The write cache will
not automatically reenable when the unit is rebuilt.
The Protection profile enables this feature, so that write cache is disabled
in the event a unit degrades; the Performance and Balanced profiles
disable this feature, so that write cache continues to be enabled.
Setting the StorSave Profile through 3DM
In 3DM, the StorSave Profile is a unit policy that can be set on the Controller
Settings page.
To set the StorSave profile through 3DM
1 Choose Management > Controller Settings from the menu bar in 3DM.
2 In the Unit Policies section of the Controller Settings page, select the
profile you want to use from the drop-down list in the StorSave column.
The page refreshes, and a message at the top confirms the change you
have made.