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
![](https://blog.armstrongconsulting.com/wp-content/uploads/2021/05/local-disk.png)
Test 2: NFS (synchronous) datastore
![](https://blog.armstrongconsulting.com/wp-content/uploads/2021/05/image.png)
Test 3: iSCSI datastore
![](https://blog.armstrongconsulting.com/wp-content/uploads/2021/05/iscsi-1024x748.png)
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).
![](https://blog.armstrongconsulting.com/wp-content/uploads/2021/05/Screenshot-2021-05-10-at-11.47.10.png)
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 🙂
And which test profile in CrystalDiskMark did you use ?
The iSCSI test looks suspiciously like the network link has changed from 10Gb to 1Gb