I have a Dell R620 running 5 500GB 7.2K RPM SATA 3Gbps 2.5in Hot-plug Hard Drives in a PERC H310 controller (which I am beginning to regret buying).
I am getting awful read/write speeds on Linux VMs (Fedora 19, Cent 6 and Ubuntu 12.04) running ESXi 5.0 free license. Using Thin, Thick or Sparse VMDKs don't make a difference.
An example hdparm:
cached reads 9750 MB in 2.00 seconds = 4877.74 MB/sec
buffered reads: 42 MB in 3.44 seconds = 12.21 MB/sec
Also a dd if=/dev/zero of=test bs=1048576 count=2048 (to create an arbitrary 2GB file) took about a minute and a half!
I have a very similar host with a software RAID controller that has similar VMs which are much faster in disk speeds. I didn't set up the RAID, I only manage the server, but IT sets them up.
The Datastore shows an average 1.189 millisecond latency for reads and a 6.3 millisecond latency for writes. The datastore shows 1.89 TB so that is about correct for 5 x 500 GB drives in a RAID 5. Initially I was thinking maybe it isn't using all of the drives. What could be going on? I have asked IT to take a look at the RAID BIOS and see if there are some diagnostics we can run.
UPDATE
I realized the one faster host has 10K RPM disks and the newer one has 7.2K
UPDATE 2
Is it possible that ESXi being run off of a SD card is causing performance to lag for disk operations within VMs?
Best Answer
The Dell PERC H310 controller does not have the ability to use write cache.
Your write performance will suffer as a result of this. This is a very bad controller for ESXi or virtualization using local disks.