Improve VDI Performance

VirtuCache: software for VMware vSphere to reduce VDI latencies

If your VDI VMs are plagued by slow application response times, long Windows boot times, cursor freezes, jittery audio/video, anti-virus software locking up VMs, performance issues for vGPU offloaded applications, and the root cause of these issues is high storage latencies from your storage network or appliance, then our VirtuCache software will be relevant.

VirtuCache solves this problem by automatically caching frequently and recently used VM data (reads and writes) from your SAN based storage to in-VMware host RAM or SSD. Subsequently, VirtuCache services more and more storage IO from this in-host cache media, instead of the IO requests traversing the storage network and served by the storage appliance. This improves VM level latencies considerably.

VirtuCache is very easy to deploy and manage. It can be installed while production VMs are running on the host, without requiring maintenance mode. You can choose to evaluate it by registering for VirtuCache download here.

VirtuCache deployment is seamless, in the sense that applications or end users don’t realize that most of the data is now read from and always first written to the in-host cache media, instead of backend storage array. Deploying VirtuCache doesn’t require any storage, network, or host reconfiguration (other than installing VirtuCache and assigning RAM/SSD to it).

Click here for technical details around how VirtuCache caches reads and writes; syncs writes to backend storage appliance; and protects against data loss in case of host failure.

We compete with all-flash and hybrid arrays, hyper converged appliances, other host side caching software, and built-in caching features in XenDesktop and Horizon View.

Versus other host side caching software.

Versus VMware’s VFRC (link with details) – VMware’s vFlash Read Cache doesn’t support VDI VMs. Also it has been end-of-lifed in ESXi 7.0.

Versus Infinio (link with details) – Infinio doesn’t support Linked Clones and non-persistent VDI. Also it only caches reads (not writes).

All the others we used to compete with like PernixData, PrimaryIO, JetStream(ex-Sandisk Flashsoft), and Samsung AutoCache are end of lifed.

Versus SSD based storage appliances and hyper-converged infrastructure(HCI).

  • Unlike an upgrade to HCI or SSD based arrays, in the case of VirtuCache, you don’t need to replace your existing storage appliance or network.
  • VirtuCache is higher performing than SSD based storage appliances because the SSD/RAM is right on the motherboard of the VMware host CPU that consumes hot data, and this cache media is connected to the host CPU over a dedicated PCIe/NVME/Memory bus. Versus in the case of storage appliances, where the SSD is behind the shared storage network and storage controllers.

  • If you choose to use in-VMware host RAM as cache media with VirtuCache, then there is no equal in performance, because storage appliances and hyper-converged boxes are not designed to use RAM in the storage IO path.
  • VirtuCache is similar to HCI in the sense that high speed storage is back in the host.
  • Unlike HCI, VirtuCache only moves the performance tier to the VMware host, the capacity tier stays in the backend array, so you still get the advantage that traditional converged infrastructure has over HCI, that you can scale and do maintenance on storage and compute independently of each other.

  • Click here for more details on how we compete with HCI like VSAN and Nutanix.

Versus built-in caching features in VMware Horizon View and Citrix Xen Desktop

Both VMware and Citrix have server side caching functionality in their respective VDI software. VMware calls it View Storage Accelerator (VSA) and Citrix calls it Machine Creation Services Storage IO Optimization (MCS IO).

But the differences between us and MCS IO / VSA are many, the top few are listed here.



VMware Horizon View Storage Accelerator (VSA)

Citrix Machine Creation Services Storage Optimization (MCS IO)

Improves the storage performance of what?

All storage IO from VDI and server VMs, and VMware kernel. Essentially all reads and writes going through ESXi are accelerated.

Only reads from Horizon View Master VM (not end user VMs) are accelerated.1

Only writes from non-persistent XenDesktop / Xenapp VMs are accelerated.2

Host cache media restrictions?

Can cache to any amount of SSD or RAM.

SSDs are not supported. Also, only a maximum of 2GB host RAM can be used.1

SSDs are not supported. Only small amount of VM memory can be assigned as cache.2

Admin Overhead.

Assign caching policy to VMs or Datastores once. No ongoing administration required.

Requires periodic ‘Regeneration’ of index, during which time VMs might be slow or inaccessible.3

VMs larger than 512GB are not supported.4

Administrator needs to manually ensure that cached writes don’t fill up VM RAM, else there will be instability/blue screen in the VMs.2,5


VirtuCache is much superior to other host side caching software and built-in caching features in XenDesktop or Horizon, so it’s not fair to compare us to these other software. The only meaningful competition are all-flash arrays. Now if you use host RAM with VirtuCache, we would be higher performing than even AFAs.

Cross references:
1-Search for ‘read cache’, ‘The cache size must be between 100MB and 2,048MB.’ on this link
2-Search for ‘writes to memory’ ; ‘only works with non-persistent VDI and RDS provisioned machines’ ; ‘blue screen’ on this link
3-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
4-Search for ‘View Storage Accelerator is disabled on virtual machines that are larger than 512GB.’ on this link
5-This happens because cached writes in RAM are never synced with backend storage, and so never evicted from VM RAM, hence the amount of writes in VM RAM keeps growing. Search for ‘actual VM disk will not have any data written to it’


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