Horizon View: Virtual Disk Digest?

Recently I was at a customer that is using VMware Horizon View for some time now, and one of the administrators asked me what the task “Configure Virtual Disk Digest” means. Once I explained this to him I thought why not write it down in a article, so here goes.

The Configure Virtual Disk Digest task will only appear in VMware Horizon View enviroments. During the creation of a Linked Clone pool or full virtual machines you got the option to enable View Storage Accelerator (VSA).

The Horizon View documentation describes VSA as.

You can configure desktop pools to enable ESXi hosts to cache virtual machine disk data. This feature, called View Storage Accelerator, uses the Content Based Read Cache (CBRC) feature in ESXi hosts. View Storage Accelerator can reduce IOPS and improve performance during boot storms, when many desktops start up or run anti-virus scans at once. The feature is also beneficial when administrators or users load applications or data frequently.

When Horizon View starts to provision (with VSA enabled on the pool) virtual desktops it will create a digest file. This file will contain indexes based on the content of each virtual disk file. At runtime, the ESXi host reads the digest files and caches common blocks of data in memory. The ESXi host cache will update the digest files at certain intervals or when a virtual machine is recomposed.

So the next time you see this task you know that VMware Horizon View is busy making your virtual desktops perform faster ;)