Points to note for VirtuCache evaluation

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  1. The hosts need to be in an ESXi cluster for VirtuCache GUI to work.
  2. If VirtuCache is installed only on one host, then Datastores won’t show in VirtuCache GUI, but the VMs will show and you can apply caching policies at the VM level. Two or more hosts should be in a cluster for VirtuCache GUI to show Datastores.
  3. ‘Write-Back with 1 Replica’ (WB1R) caching policy caches reads + writes, and mirrors the writes to cache media in another host in the same ESXi cluster. This is to protect against data loss if the host fails. Below are the requirements for WB1R policy.
    • You need to install VirtuCache on all hosts in the VMware cluster and the same VirtuCache build has to be installed on each host.
    • Replication network needs to be configured in the ‘Hosts’ tab in the VirtuCache GUI. By default we use vmotion network for write replication, but you can create a private network for write replication.
    • Make sure that you use the ‘default’ VMware TCP/IP stack, and not VMware’s ‘vMotion’ TCP/IP stack on the network you choose for write replication. vMotion stack doesn’t let any traffic other than vMotion traffic go over this network.
    • For very low write latencies, 10gps network with Jumbo Frames and LACP is preferred (though not required).
  4. Write-Through caching policy
    • Only caches reads, not writes.
    • It uses the Replication network for moving small amounts of read cache on as needed basis when a VM does a vMotion . So the Replication network still needs to be configured using the ‘default’ VMware TCP/IP stack like in #3 above. Only read redirects are not bandwidth intensive, and so a 1gbps VMware network will suffice.
    • You don’t need VirtuCache on all hosts in a cluster, but the hosts that have VirtuCache installed, should have the same VirtuCache build.
  5. Only use enterprise grade SSDs and not consumer SSDs. Consumer SSDs have poor latencies for random IO.
  6. You can cache to RAM or SSD or both.
  7. If you plan to use a SSD as cache device, we prefer that you use NVME or PCIe SSDs since that avoids Queue Depth related issues.
  8. If you use SATA or SAS SSD. Please configure the SSD as RAID 0, even if its a single SSD; use a high queue depth RAID controller;  and tag the RAIDed SSD as ‘device type’ =  ‘flash’ in vCenter. RAID0 of SSD assigns it a high queue depth.
  9. Do not use WB2R policy, unless you have more than 8 hosts in a cluster and 20gbps for write replication network.
  10. Backup-VM policy is to be applied to Veeam (or similar backup software) management and proxy VMs.

The most common reasons for VirtuCache not improving performance are high SSD latencies (reasons 5 and 8 above) and high network latency (because of reason 3 above).

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