3Ware 9550SXU-12 User Manual page 136

Configuring Units
Table 9: StorSave Profile Definitions
Definition
FUA (Force Unit
Access)
Write Journaling
Disable Cache on
Degrade
124
About StorSave Profile Levels
The three profiles automatically adjust several different factors that affect
protection and performance on a per unit basis. These are summarized in the
table below and further explained after the table.
Protection (Default)
Maximum data
protection, but slower
performance.
Honor FUA (If no BBU is
present)
Ignore FUA (If BBU is
present)
Enabled
Enabled
• FUA (Force Unit Access)
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 has the FUA bit set, 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 the FUA bit.
The Protection and Balanced profiles honor FUA commands if no BBU is
present; the Performance profile ignores them regardless of whether a
BBU is present.
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 tracks the writing of data to disk and
Write Journaling
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.
3ware SAS/SATA RAID Software User Guide, Version 9.5.1
Balanced
More data protection than
Performance but less
data protection than
Protection.
Honor FUA (If no BBU is
present)
Ignore FUA (If BBU is
present)
Disabled, if no BBU
present. (Enabled, if BBU
is present.)
Disabled
. The FUA bit is a way that the RAID
Performance
Maximum performance
for the unit, but less data
protection.
Ignore FUA
Disabled (If BBU is
present, this essentially
disables the BBU for this
unit.)
Disabled