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View Storage Accelerator vs. VirtuCache – VMware Host Cache

The big difference between the two is that VSA caches only 2GB of reads from the Master VM1,2. VirtuCache caches reads + writes from all server & desktop VMs, and it can cache to TBs of in-host SSD/RAM, so all storage IO is serviced from in-host cache.

More details in the table below.

Feature

VirtuCache

View Storage Accelerator

Works for server and VDI VMs.

Yes.

No. Works only with Horizon View VDI. Does not work for server VMs or non-VMware VDI like Xen Desktop.

Caches to host RAM.

Yes. No restriction on amount of RAM that can be used.

Yes. Can cache to a maximum of 2GB RAM only.2

Caches to in-host SSD.

Yes. No restriction on amount of SSD capacity that can be used. If both RAM and SSD are used, then the cache is tiered between RAM and SSD.

No.2

Improves performance of VM reads (caches reads).

Yes. All reads from VMs (server and VDI) are cached.

Only data that is shared across all Horizon View VDI VMs (common blocks) are cached, so only a subset of reads from master VM are cached.3

Improves performance of VM writes (caches writes).

Yes. All writes from VMs (server and VDI) are cached.

No.2

Speeds up VM creation and deletion.

Yes, because VirtuCache caches IO originating in the ESXi kernel. VM provisioning and deletion are ESXi kernel processes.

No.

Admin Overhead.

Assign caching policy to VMs or Datastores once.

No ongoing administration required after.

Requires periodic ‘Regeneration’ of index, during which time VMs might be slow or inaccessible.4.

VMs larger than 512GB are not supported.5

Turning on VSA requires recompose.

Typical customer configuration and cost.

$3000 per ESXi host for perpetual license. Typically, our customers use a 2TB NVME/PCIe SSD as cache media per host.

Bundled with Horizon View. Typically the maximum amount of 2GB RAM is assigned to VSA on a per host basis. 4

Though View administrators compare us to VSA, please compare price/performance of VirtuCache to an all-flash array instead, since the storage acceleration VirtuCache provides is across all your VMs, and it is typically configured to use larger amounts of cache media than VSA. This ensures that most of the IO is served from in-host cache media, making VirtuCache performance closer to all-flash arrays.

VMware authored cross-references.
1 – Search for ‘read common data blocks from cache’ on pg 39 of this PDF https://docs.vmware.com/en/VMware-Horizon-7/7.4/horizon-architecture-planning.pdf
2 – Search for ‘read cache’, ‘The cache size must be between 100MB and 2,048MB.’ on this link https://docs.vmware.com/en/VMware-Horizon-7/7.4/horizon-administration/GUID-77B22AC9-EF9F-4161-9856-88DADEE095DD.html
3 – Search for ‘Common Blocks’ in https://docs.vmware.com/en/VMware-Horizon-7/7.0/com.vmware.horizon-view.desktops.doc/GUID-84AB0AD4-CE68-4D40-B63A-8011586EB16E.html
4 – Search for ‘View Storage Accelerator might take tens of minutes to generate or regenerate the digest files for large virtual disks (for example, a 100 GB virtual disk). As a result, the desktop might be inaccessible for longer than expected.’ on this link https://docs.vmware.com/en/VMware-Horizon-7/7.3.3/rn/horizon-733-view-release-notes.html
5 – Search for ‘View Storage Accelerator is disabled on virtual machines that are larger than 512GB.’ on this link https://docs.vmware.com/en/VMware-Horizon-7/7.3.3/rn/horizon-733-view-release-notes.html