LSI 3ware SAS 9750-8i Guia do Utilizador descarregar pdf (Página 131)

Setting Unit Policies

www.lsi.com/channel/products 119

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.

• 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.

Table 9: StorSave Profile Definitions

Protection Balanced (Default) Performance

Definition

Maximum data

protection, but slower

performance.

More data protection than

Performance but less

data protection than

Protection.

Maximum performance

for the unit, but less data

protection.

FUA (Force Unit

Access)

Honor FUA (If no BBU is

present)

Ignore FUA (If BBU is

present)

Honor FUA (If no BBU is

present)

Ignore FUA (If BBU is

present)

Ignore FUA

Write Journaling

Enabled Disabled, if no BBU

present. (Enabled, if BBU

is present.)

Disabled (If BBU is

present, this essentially

disables the BBU for this

unit.)

Disable Cache on

Degrade

Enabled Disabled Disabled

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