emryl

Do you tried passthrough the SATA controller in order to be able to access the disks instead of RDM? I have a similar setup and don't passthrough the controllers. I just create a vmfs datastore, create virtual disks which I then pass to the xpenology vms. Has been performing well and stable for a very long time.

Performance will degrade if you choose thin provisioning and the transfer keeps filling up available space on vmfs. The process for claiming new chunks of space is expensive. That would explain your slowing down, especially since you are on a lower spec rig (Microserver). For increased performance, try putting your volumes on NFS, or pre-allocate the full disk size or go the RDM route as stated previously.

I've got the same issue on both 5.1 and 5.5. I'm using a mix of raw mappings and virtual disks. Using the paravirtual driver and the Trantor release of 4.3. Writes have this problem but reads seems not affected. I've haven't looked into the issue but would be willing to share thoughts.