Avago Technologies 3ware SAS 9750-16i4e - Manual (Page 75)

Controller Object Commands
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When a verify background task is active, if the task rate is set to a fast verify
rate (i.e., low I/O rate), the system latency increases and performance can be
negatively affected, especially for applications such as video server
applications and audio applications. The Low Latency setting minimizes the
latency (delay) in reading data from the RAID unit by slowing down the
rebuild task, which allows host Reads to complete, thus improving
performance.
For a more complete discussion of background task modes, see “Working
with the Background Task Mode” in the 3ware SATA+SAS RAID Controller
Card Software User Guide, Version 10.2.
Example:
//localhost> /c1 set verifymode=lowlatency
Setting Verify background task mode of /c1 to [lowlatency] ... Done.
Related commands:
/cx show verifymode
/cx set verifyrate=<1..5>
/cx show verifyrate
/cx set verifyrate=<1..5>
The /cx set verifyrate command sets the verify task rate of the specified
controller. The verify task rate sets the verify execution priority relative to I/O
operations.
This task rate is in the range of [1..5], where 5 denotes the setting of fastest
background task and slowest I/O, as follows:
5 = fastest verify; slowest I/O
4 = faster verify; slower I/O
3 = balanced between verify and I/O
2 = faster I/O; slower verify
1 = fastest I/O; slowest verify
Example:
//localhost> /c1 set verifyrate=2
Setting Verify background task rate on /c1 to [2] (faster I/O)
... Done.
Important: Setting verifymode to low latency and verifyrate to 5 is not
recommended when I/O is active because, in that case, the verify as a background
task might never complete. Use this setting with care.