Avago Technologies 3ware SAS 9750-16i4e - Manual (Page 172)

Chapter 8. Maintaining Units
160 3ware SATA+SAS RAID Controller Card Software User Guide, Version 10.2
tasks with host I/Os to maximize the speed of both host I/O and background
tasks.
If latency is not an issue in the applications you use, then using the Adaptive
Background Task Mode will probably meet your needs and will result in
background tasks that complete faster.
Relationship of Task Mode and Task Rate
The Background Task Mode works in conjunction with the Background Task
Rate. The settings are shown in Figure 79.
Figure 79. Background Task Settings on Controller Settings page
Background Task Rate lets you set the relative performance of background
tasks in relation to host I/O activity on a scale of 1 to 5 , with 5 being the
fastest background task and slowest I/O, while 1 is the fastest I/O and the
slowest background task, as shown in Figure 79. Separate settings are
available for Rebuild/Migrate and for Verify. (Initialization occurs at the
Rebuild/Migrate rate.)
5 = fastest background task; slowest host I/O
4 = faster background task; slower host I/O
3 = balanced between background tasks and host I/O
2 = faster host I/O; slower background task
1 = fastest host I/O; slowest background task
If you set the Background Task Mode to Low Latency , it slows down the
background task process in the context of the current Task Rate setting, with a
graduated pacing of host I/O versus background task I/O, 2 through 5.
Important: It is recommended that if you use the Background Task Mode of
Low Latency, you always set the Background Task Rate to at least 2 on the
scale of 1 to 5. When used in conjunction with a rate of 1 (fastest host I/O;
slowest background task), Low Latency Mode can create a situation in which
background tasks never complete, if there is continuous host I/O activity on
the unit.
If you do select Low Latency when the Rate is set to 1, 3DM2 will display a
warning, and will then continue to display a recommendation to change it
until you change either the Rate to
2 or greater, or until you change the Mode
to Adaptive (Figure 80).