Slow performance with write heavy applications

[vector_it]

We are currently running VMware ESXi 5.0 on a Dell PowerEdge R815.  For our storage device we are using an connection  iSCSI to a Dell EqualLogic PS4100X.  We are attempting to run 80 Windows vm's (20 per datastore, datastores on the SAN) that write a lot of data to the disk.  As a result we are seeing performance issues on the EqualLogic due to the high number of iops.  Can anyone recommend ways to prevent excessive iops or other perfomance bottlenecks?  Is running the vm images from a local disk better than off the SAN? 

[rickardnobel]

How many disks are on the iSCSI SAN? What RAID level are you using? Do the LUNs share the same physical disks?

One likely reason could be that you have a certain limit of random write IO from the number of physical disks and the need from your VM is larger than this. Storing VMs on local disk could spread the IO load somewhat, but also make other important features break like HA.

[vector_it]

rickardnobel we have 22 10k SAS drives in our iSCSI SAN.  We are using RAID 50.  As far as I know the LUN's are distributed among all 22 disks.  The local disks in the vmware server are 7.2k SATA drives.  We do not require the HA feature for these vm's.  Any recommendations are greatly appreciated.  Thanks.

[taylorb]

22 Disks is what I would often recommend for a SINGLE random write heavy application.  And RAID 50 is a poor choice for write intensive application. You've way under spec'ed your storage if you are trying to run 80.   You are probably only talking 1000 IOPS with 22 10K disk in a RAID 50.   You could double your write performance if you swap to RAID 10, but even then you really probably need 100 spindles to even have a prayer.  

Just based off what you mentioned in your OP about 80 write intensive VMs, I'd be recommending 100+ 15K disk and RAID 10 as a starting point.  .