I have an iSCSI HP P2000 loaded with 12 x 300gb DP SAS drives. This is connected to 2 DL385 servers with 64gb RAM running XenServer. The SAN network is multipathed via 2 gigabit switches (4 x copper links from the P2000 to each switch, then each XenServer has a copper link to each switch)
Recently I re-evaluated my install-time decision to create 2 vdisks: a RAID-5 and a RAID-10. I decided the RAID-5 was pointless and destroyed it, then used those disks to extend the RAID-10 into one big array, with 2 hot-spare disks.
Since that was done (just over a week ago) disk performance has been quite horrible; looking at
top on both the XenServer hosts show ~15% I/O wait. hdparm inside a VM shows around
1.12MB/s reads from the SAN.
There are 2 other Win2008R2 machines connected to the SAN also. I have previous performance tests showing they too are experiencing a significant difference so I don't believe it is a problem on the XenServer hosts.
- 8k random reads previously
- 64k random reads previously
The RAID extension has completed, everything is "OK" in the SMU. The XenServers are quite "empty" (7 VM's on one of them, 4 VM's on the other) but it is a production environment.