I got a vmware esxi 5.5 on a Dell PowerEdge R710 with 6 sata disks in RAID5 with a single logical volume on a Perc H700 controller. Vmware is installed on this Raid5 volume and also the virtual machines run on the same volume.

I noticed that when I try some storage benchmark on vm I got a good read/write throughput (100-150 MB/s), but I have an high latency and in general I noticed that vm aren't fast as I'm expect (the server has 2 Quad core Xeon CPU with 48 GB or ram).

I always read comments about vmware best practices which recommend to not run vm on the same datastore where vmware is installed, I also read about some caching issue about that (vmware disable caching on its installation volume), but I never found any detailed information about this on vmware knowledge base (except generic guidelines, something like 'this is not the best practice' without any technical explanation).

Do you have some tecnical informations about that or have you found something more specific about this behavior?

Do you think this latency (and in general this clumsy performance) can be solved creating a new volume on the same controller (ora a single disk on the same controller outside the RAID array) and installing vmware on that volume or disk?

Thanks for any information


  • How fast are the disks (RPM of spindles, which SSD)? Which benchmark, what IOPS are you trying to achieve with it? Note that several people avoid RAID5 due to the risk of losing another when rebuilding the array. – John Mahowald Jan 12 '17 at 12:45
  • 10k rpm SAS. I don't have a specific objective in IOPS, I only noticed these vm are quite slow; now I downloaded the vmware 6.0 iso from Dell support website, I read about other people with similar problems, I'll try to upgrade to this one and see if I notice some difference (my vmware instance came directly from vmware site), it should contain specific drivers for perc controllers. – Bill Guarnere Jan 13 '17 at 22:22

There's nothing wrong with what you have now. It's okay to have VMware on the same disks as your VM datastore volume in single host installations.

I personally choose to create a small logical drive (or virtual drive) of 16GB on the hardware RAID controller to install ESXi on. This is cleaner for upgrade and support reasons, but isn't necessary.

As far as performance, throughput isn't everything. Latency definitely matters more. Does your H700 controller have a Battery-Backed write cache unit?

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  • I installed openmange vib and check the raid controller, it has an active battery and virtual drive in write-back mode. – Bill Guarnere Jan 13 '17 at 22:18

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