Setting the StorSave Profile for a Unit

You can set the desired level of data protection versus performance for a unit by selecting the StorSave Profile. Three profiles are provided: Protection (maximum data protection), Performance (maximum performance, less data protection), and Balanced (a middle ground).The default is Protection.

Note: If the write cache setting is disabled for a unit, the StorSave Profile capability does not apply and is automatically disabled.

About StorSave Profile Levels
To set the StorSave profile

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.

StorSave Profile Definitions

	Protection (Default)	Balanced	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

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 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.

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.

To set the StorSave profile

Choose Management > Controller Settings from the menu bar in 3DM.
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.

Copyright (c) 2004-2006, AMCC