3Ware 9550SXU-12 User Guide - Page 136
About StorSave Profile Levels, Table 9: StorSave Profile Definitions
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Configuring Units 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. Table 9: StorSave Profile Definitions Definition FUA (Force Unit Access) Write Journaling Disable Cache on Degrade Protection (Default) Balanced Performance Maximum data protection, but slower performance. Honor FUA (If no BBU is present) Ignore FUA (If BBU is present) Enabled Enabled More data protection than Performance but less data protection than Protection. Maximum performance for the unit, but less data protection. Honor FUA (If no BBU is present) Ignore FUA (If BBU is present) Ignore FUA Disabled, if no BBU present. (Enabled, if BBU is present.) Disabled (If BBU is present, this essentially disables the BBU for this unit.) Disabled Disabled • FUA (Force Unit Access). The FUA bit is 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 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. 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. 124 3ware SAS/SATA RAID Software User Guide, Version 9.5.1