Write-Back Caching

01 Jan: VMs with Duplicate BIOS UUIDs when using Datrium Cloning

VMware VMs have two UUIDs – BIOS UUID and instance UUID. VirtuCache doesn’t support Write-Back policy where multiple VMs in the same vCenter share the same BIOS UUID, even if these VMs have different Instance UUIDs. When using the cloning feature in Datrium (now end of lifed), the cloned VM…

18 Nov: VMs not in Write-Back mode because of Multi-Writer VMDK

In rare cases, one or more VMDKs on a VM could have its ‘sharing’ field (drop-down field in ‘Edit Settings’ at the VM level) set to multi-writer, in which case it is not possible to move that VM to Write-Back caching mode. Such VMs can only be set to ‘Write-Through’…

25 Mar: In case the Write-Replication network fails

If the write-replication network fails, then VirtuCache keeps trying to replicate writes for 30seconds, during which time writes are not being acknowledged. After the 30 second period, VirtuCache times out the writes. Then VirtuCache freezes IO till the write cache is synced with backend SAN. Since we keep upto 2…

13 Mar: VMs not in Write-Back mode because of Replication Network issues

Caching policy of ‘Write-Back 1 Replica’ is assigned to VMs or Datastores, but the operational state remains ‘Write-Through’. The reasons could be one or more listed below. The VirtuCache replication network is the vmotion network and the vmotion network might be using the vmotion stack that precludes all other traffic from…

01 Mar: VMs not in Write-Back mode because they might be on local storage

VM might show operational state of Write-Through even though its caching policy is Write-Back,  because the VM might be on local storage or NAS storage and not on SAN storage. In this situation the caching policy will show as Write-Through, but no caching will actually happen, because VirtuCache doesn’t cache…

22 Dec: vMotion between hosts that are in two different datacenters

A stretched VMware cluster is configured across two different datacenters/sites connected over a WAN link, and VM vmotions can happen over the WAN link between hosts at these two site locations. If you are using ‘Write Back’ policy and if you want to support live VM vmotions between hosts across…