This past week I installed an EMC VNXe 3100, the install went well and the new Unisphere Interface made it a snap to get the VMware ESXi boxes added. One of the requirements was to have some RAID10 space and make the rest RAID5, and because of the way the VNXe creates storage pools and the number of disks that I had to work with I created a 6 drive RAID10 pool (the minimum # of drives for RAID10) and a 15 drive RAID5 pool.
Then I got to thinking… would 6 drives in RAID10 really out perform 15 drives in RAID5?
Let me back up for a minute and explain why the requirement for RAID10 is there. Before the migration to virtualization, the customer had in place a SQL cluster that used an older SAN for shared storage. The goal with the new equipment was to create a high IOps LUN that we could migrate that SQL data to and still maintain good performance… which is why RAID10 was thought to be the best option.
So now that the hardware is installed and we can test some real-world numbers I thought we might as well see if giving up all that extra drive space for RAID10 was really going to get us more IOps.
First here is the RAID5 performance, this is on the VNXe3100 with a 15 drive RAID5 storage pool divided up into several VMware datastores. The IOMeter config that was used was downloaded from the VMKTree.org site and is the same one that I’ve used for the other SAN testing that I’ve done.
Note: All drives are 300GB 15K RPM 3.5″ Drives.
And here is the RAID10 performance with 6 drives
So after seeing these results, I wonder if RAID10 storage is really needed? Obviously, if we had the exact same spindle count for RAID5 as RAID10 then RAID10 would have been faster. But for an SMB situation like this I think that we would be better off removing the RAID10 pool, and adding 5 more drives into the RAID5 pool. Realistically we would be able to achieve higher performance with a 20 drive RAID5 then a 6 drive RAID10. Plus we can make more space used for future needs.
There are situations that I can think of where RAID10 would still be required even if RAID5 performance is just as good, and that is when a software vendor requires it… some even won’t support their application unless its on RAID10, so the bottom line checks your software manuals… make sure RAID10 isn’t mandatory before switching everything to RAID5.