Hello -
I'll try to keep this as short and sweet as possible. We have 2x hypervisors hosting 4x virtual SQL Servers per physical hypervisors, so:
VMHOST01 - SERVER01 VMHOST02 - SERVER05
VMHOST01 - SERVER02 VMHOST02 - SERVER06
VMHOST01 - SERVER03 VMHOST02 - SERVER07
VMHOST01 - SERVER04 VMHOST02 - SERVER08
We chose to partition our MD3200 storage array similar to how we would have partitioned it if these were physical servers, so we have 48 disks in our MD3200, which yields 8 RAID-5's of 6 disks a piece. Pretty simple so far. But we're seeing some weird performance, and I wonder if it's due to the high number of small RAID volumes. Keep in mind that the MD3200 is a pretty entry-level dual-controller SAS 2.0 SAN.
Using simpleton logic, one would think the RAID controllers in the SAN wouldn't care whether it was 48 disks split 12 ways, or 48 disk split 4 ways, but I'm beginning to think there's a performance implication. Does anyone have any experience will Dell storage to know if we might see better performance in just cutting 4x RAID-5 volumes, then just having the virtual disks "share" the same VMFS volume?
We thought the RAID controller perform better if it was aware of the "sharing" (i.e. because it was managing each individual LUN), but now I'm starting to think that the RAID controller is getting overwhelmed by the number number of small volumes, and maybe VMWare would do a better job managing the sharing if the VMFS volumes between VMs.
Keep in mind these are SQL Servers with heavy I/O. I would test it out, but with the volumes actively being used and more than 50% full, it's next to impossible to rejigger everything around to free up two full RAID volumes to combine.
Thanks,
- Jeff