Avago Technologies 3ware 9650SE-12ML (Channel) - Manual (Page 11)

Working with the Background Task Mode
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Working with the Background Task Mode
Background tasks are maintenance tasks that help maintain the integrity of
your drives and data. These tasks include
• Initialization of units
• Verification of units
• Rebuilds when units have become degraded
• Migration of an online RAID unit from one RAID configuration to
another
• Self-tests
3ware RAID management software includes some controls to help you
balance completion of these tasks with host I/O responsiveness, so as to
minimize any conflict between the two. For example, you can schedule when
backgrounds tasks should be run (to avoid peak work hours) and you can
specify the rate at which they run in relationship to foreground I/O tasks.
In 9.5.2, a new feature—Background Task Mode—has been added to the
existing Scheduling and Rate controls. Background Task Mode is specifically
designed to address the issue of latency, which can cause problems for some
applications, by helping you balance the rate of host I/O and efficient
completion of background tasks.
About Latency and the Background Task Mode
Latency is the real or perceived delay in response time seen by the host
system when accessing some data. For some applications, such as streaming
video and audio application, it is important to minimize the latency of read
commands, so that users do not perceive a lag when viewing video or
listening to audio.
When background tasks are active (for example, rebuild, verify, and
initialization), there can be increased latency, and under some circumstances,
this can result in a degraded user experience or in an application failure.
You can set the Background Task Mode to minimize latency. This mode
monitors and paces the relationship between host I/Os and background tasks.
You can set the Background Task Mode to either
Adaptive (the default) or
Low Latency .
Note: This section provides information about the Background Task Mode setting.
For additional information about background tasks and related controls, see the
section “Background Tasks” in Chapter 9, “Maintaining Units” in the 3ware SAS/
SATA RAID Software User Guide, Version 9.5.1..