VM disk performance across datastores

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Here are some disk performance measurements (made on a Windows 10 VM on vSphere 6.5 with CrystalDiskMark) across different types of datastore (local SSD array, NFS (sync), NFS (async) and iSCSI).

The NFS and iSCSI datastores were on a Synology RS3412xs with 7x 2TB Samsung 860 EVO SSDs in a RAID5 volume. The vSphere host was connected to the Synology with 10Gbe.

The vSphere host was a Dell 720 with a PERC H710 mini disk controller (with battery-backed cache) and 4x 2TB Micron 5100 SSDs in RAID5.

Note: Test 4, using asynchronous NFS, is not relevant for real-world VMs because a power failure is likely to corrupt VM file systems on asynchronous NFS volumes.

Test 1: Local SSD array datastore

Test 2: NFS (synchronous) datastore

Test 3: iSCSI datastore

Test 4: NFS (asynchronous) datastore

Note! only included for comparison – async NFS is not suitable for production VMs (since a power failure will corrupt the VM’s file system due to the fact that file systems journaled writes may not be flushed to disk).

3 thoughts on “VM disk performance across datastores

  1. Dennis B.

    Hey Roger,

    did you notice any load problems on the synology when disabling “async” on the nfs share ?
    I got similar “ok” performance on a RS4021xs+ over nfs with async, but the system was nearly unusable when i disabled async.
    With async disabled the load average of the synology would rise above 10 within 30 seconds and perfomance would drop down to15-30mb/s on writes…

    Our setup is
    13x 10TB WD Red (Raid6)
    2x 1TB SSD Cache (Raid1) yeah i know this drops our raid level overall 🙂


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