3+1P versus 7+1P RAID5 Comparisons on the XP Array

[Alzhy]

Has anyone done any performance comparison (Oracle use) between a 3+1P RAID5 Config and a 7+1P RAID5 Config on the XP arrays (1024 or 12000)?

On true Hitachi arrays, we saw vey little difference between a RAID1 (2+2) and a RAID5 (3+1P). However, I am curious as to the difference between a 3+1P config and a 7+1P...

Anyone?

[Patrick Wallek]

If I am reading this right, the 3+1P will be 3 disks plus the parity disk and 7+1p will be 7 disks plus 1 parity.

Some potential benefits I can see -- with 7+1P you will have data striped over 7 disks, potentially increasing some throughput, plus if the whole array is 7+1P you should see more usable capacity as you have 1 out of 8 disks for parity instead of 1 out of 4.

[Alzhy]

I've thought of that as well Patrick but onthe writes - I think the 3+1P setup comes very close to a RAID1 (2+2). True, 7+1P yields 87+% space usability over 3+1P's 75% and 2+2's 50% efficiency but our environments are pretty write intensive.

On an earlier Hitachi frame, we actualluy performec tests with 2+2 configs and 3+1P configs and picked the 3+1P for its performance and more usable space. The way we do volume management on the host/server end is we actually stripe LUNs from each ACP's array group.