3Ware 9550SXU-16ML User Guide - Page 150

FUA Force Unit Access, Write Journaling, Write cache disabled on degrade

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Chapter 8. Configuring Units „ 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. 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 when the disk drive will only issue 'command complete' to the controller once the data is written to media. The Protection and Balanced profiles honors FUA commands; the Performance profile ignores them. If you use a battery backup unit (BBU), FUA is ignored, because the BBU preserves the contents of the controller cache memory for a limited period of time (up to 72 hours), in the event of a power failure. „ 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 Profile disables it. The Balanced profile disables it only if no BBU is present. If write journaling is disabled and a BBU is present, then it is as if the BBU was disabled for that unit. „ 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 using 3DM2, 3BM, or the CLI. The write cache will not automatically reenable when the unit is rebuilt. The Protection profile enables this feature, so that write cache is disabled; the Performance and Balanced profiles disable this feature, so that write cache continues to be enabled. 140 3ware 9550SX Serial ATA RAID Controller User Guide

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Chapter 8. Configuring Units
140
3ware 9550SX Serial ATA RAID Controller User Guide
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.
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 when the disk drive will only issue
'command complete' to the controller once the data is written to media.
The Protection and Balanced profiles honors FUA commands; the
Performance profile ignores them.
If you use a battery backup unit (BBU), FUA is ignored, because the BBU
preserves the contents of the controller cache memory for a limited period
of time (up to 72 hours), in the event of a power failure.
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 Profile
disables it. The Balanced profile disables it only if no BBU is present.
If write journaling is disabled and a BBU is present, then it is as if the
BBU was disabled for that unit.
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 using 3DM2, 3BM, or
the CLI. The write cache will not automatically reenable when the unit is
rebuilt.
The Protection profile enables this feature, so that write cache is disabled;
the Performance and Balanced profiles disable this feature, so that write
cache continues to be enabled.