Avago Technologies 3ware SAS 9750-16i4e - Manual (Page 213)

Controller Settings page
www.lsi.com/channel/products 201
Background Task Rate and Mode
Two Background Task settings allow you to control the balance of
background tasks and I/O (reading and writing to disk) performed by the
controller.
Background Task Rate lets you set the ratio at which background tasks are
performed in comparison to I/O, on a scale from 5 to 1.
There are separate settings for Rebuild/Migrate Rate and Verify Rate. The
Rebuild/Migrate Rate also applies to initialization. Although the same rate is
used for rebuilding, migrating, and initializing, migrating has the highest
priority.
For additional information, see “Setting Background Task Rate” on page 162.
Background Task Mode works with Background Task Rate, to address the
issue of latency. Two settings are available: Adaptive (the default) and Low
Latency .
Low Latency mode minimizes the latency (delay) in reading data from the
RAID unit by slowing down the background task process. In contrast,
Adaptive mode allows the firmware to adjust the interaction of background
tasks with host I/Os to maximize the speed of both host I/O and background
tasks.
For additional information, see See “Working with the Background Task
Mode” on page 159.
Unit Policies
On the 3DM2 Controller Settings page you can enable or disable these
policies:
Write Cache , Auto-verify, Overwrite ECC, and Queuing You can
also choose a StorSave Profile and change Rapid RAID Recovery settings .
Write Cache. When write cache is enabled, data is stored locally in memory
on the drive before it is written to the disk drive media, allowing the computer
to continue with its next task. This improves performance. However, in the
event of a power failure, the data in the controller's write cache will be lost if
you do not have a battery backup unit (BBU) or an uninterruptable power
supply (UPS).
For additional information, see “Enabling and Disabling the Unit Write
Cache” on page 102.
Read Cache. The Read Cache unit policy lets you enable either Basic read
caching or Intelligent read caching. You can also disable the Read Cache unit
policy, if preferred. By default, Read Cache is set to Intelligent .
Intelligent read caching includes a typical read-ahead caching method which
is used to proactively retrieve data from media and store it locally on the
controller with the anticipation that it may be requested by the host, and also