Accusys ExaSAN B08S2-PS - Manual (Page 72)

4. How to Use
User Guide Page 4-21
Note
Although slow responds of some hard disks can be tolerated in DLP mode,
you may use S.M.A.R.T. function to check the conditions of hard disks in an
array and replace the faulty ones.
Note
This function does not support JBOD and NRAID.
NCQ (Native Command Queuing) – This mode is designed for increasing disk drive access on SCSI and
SATA disk drives. It can do this under certain situations by allowing the individual hard disk to internally
optimize the order in which it executes the read and write requests it receives. This can reduce the amount
of unnecessary drive head movement and resulting in better performance for work loads where multiple
read/write requests and outstanding at the same time.
This situation most often occurs in server-type applications. However, the current technology actually
slows down disk drive access in certain applications, such as video editing and sequential reads and
writes, because of the added latency induced by NCQ.
Figure 60: NCQ concept
The figure above illustrates the access sequence in NCQ and non-NCQ mode. The content sequences of
the two hard disks are the same: 1, 2, 3, 4. However, the access sequence in NCQ mode may vary to
improve the performance.
Note
If Equalization mode is enabled, NCQ is automatically turned off.
SMART Mode – S.M.A.R.T. is a monitoring system of disk drives to detect and report on various
indicators of reliability, in the hope of anticipating failure. ExaSAN RAID system supports S.M.A.R.T.
Once this function is selected, you can select the check interval from the drop-down list. Choose from 1
minute to 8 hours for SMART Mode to be active. The RAID controller will command each hard disk to
perform S.M.A.R.T. according to the check interval selected. The check results will be shown as an Event
message in the main menu.