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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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2  
Do you have a write-caching battery or flash module on the controller? –  ewwhite Sep 26 '13 at 14:50
    
I believe this PERC H310 doesn't have those abilities, it is an entry level controller. –  user160910 Sep 26 '13 at 16:56
    
Spec sheet for PERC H310 i.dell.com/sites/doccontent/shared-content/data-sheets/… –  user160910 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

1 Answer 1

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.

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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? –  user160910 Sep 26 '13 at 18:11

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