Release Notes

47 Analyzing Dell PS Series Storage with SAN Headquarters | TR1050
This Live View sample shows I/O spikes of over 1000 and a few latency spikes. The latency spikes correspond to larger
I/O sizes (as expected). In this case, Live View is providing a more detailed picture of the ESRP I/O profile. Although the
spikey behavior when shorter intervals are measured is evident, this does not necessarily represent a problem. More
accurately, these spikes should be considered when sizing to solutions close to the maximum capabilities of the array.
3.6 Example 6: Raid Evaluator
SAN HQ includes a reliability-modeling tool known as the Raid Evaluator. The Raid Evaluator provides expected relative
reliability based on the current RAID Policy and the expected performance with different RAID policy choices.
In the ESRP test, the administrator wanted to gain usable capacity by changing to a RAID 6 configuration. In order to
model this change the possible RAID Policy was changed to a RAID 6 from RAID 10 which is the current RAID Policy. This
provides the additional capacity and a higher relative reliability score since now two parity disks are available in the
event of a hard drive failure.
Figure 33 RAID Evaluator showing higher reliability; however Possible Max IOPS are lower
Notice the right side of the dashboard models the expected possible maximum IOPS from a RAID policy change. Since
modifying the RAID policy from RAID 10 to RAID 6 would increase the number of writes to the disks, we would expect
the estimated maximum IOPS to be lower. See Table 3 for the write penalties based on RAID policy.
The RAID evaluator models the differences that RAID choices have on performance. Since RAID 6 requires more I/O for
writes the maximum IOPS growth is -50% for the time interval selected. For this example, changing the RAID policy may
have an adverse effect on the performance.
Note: Verify the possible impact on performance before changing the RAID policy