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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?

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    Do you have a write-caching battery or flash module on the controller? – ewwhite Sep 26 '13 at 14:50
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    I believe this PERC H310 doesn't have those abilities, it is an entry level controller. –  Sep 26 '13 at 16:56
  • Spec sheet for PERC H310 http://i.dell.com/sites/doccontent/shared-content/data-sheets/Documents/dell-perc-h310-spec-sheet.pdf –  Sep 26 '13 at 16:59
  • This doesn't answer your question but you probably want the PERC H710, H710P or H810. – joeqwerty Sep 26 '13 at 17:19
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    @GreggLeventhal No, using ESXi on USB isn't slowing you down. – ewwhite Sep 27 '13 at 14:50
  • @GreggLeventhal To add to ewwhite's statement, I've seen it possible to remove the SD or USB drive that loads ESXi and still have the host and all the guests continue to run fine until the next reboot as it loads it almost all it needs to run the hypervisor into memory. – Rex Sep 27 '13 at 14:59
  • What I don't get is how you managed to run ESXi with a software RAID controller - I do not know of a single supported model for ESXi. – the-wabbit Feb 03 '14 at 10:43
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    I've recently had the 'pleasure' of working with a couple of Hyper-V hosts using 4x 7.2K NLSAS disks in RAID-5 with these controllers. I gotta say, the H310 is probably fit to use to stir paint, but not much more than that. – Evan Anderson Jan 27 '15 at 20:00

2 Answers2

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The Dell PERC H310 controller does not have the ability to use write cache.

H310 — Entry hardware RAID controller. Provides entry-level performance with no cache. RAID5 functionality with modest performance.

Your write performance will suffer as a result of this. This is a very bad controller for ESXi or virtualization using local disks.

ewwhite
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    I realized the problem.. The first host has 10,000 RPM disks and the new one has 7.2K, so comparing them is useless. I suppose the performance is as expected given 7.2K disks and a mediocre controller? –  Sep 26 '13 at 18:11
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Remember that with RAID, the RAID turns off the built in disks cache memory, so you with a PERC H310 are running with no read buffer/write buffer except provided by the OS.

A raid controller without the memory is useful for JBOD, ( with the caches on ), and mirroring, and less than useful with RAID 0 ( striping ) or RAID 5 ( Striping with parity ) caches off.

the 10K drives make a world of difference.

David Makogon
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ForOldHack
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