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PernixData’s FVP vs. Virtunet – Both VMware Kernel Write Caching Software

More similar than different

Both us and PernixData differentiate from rest of the host side caching vendors in similar ways - that we are kernel mode software; both of us cache writes in addition to reads; have data protection strategies in place to prevent against data loss in case of multiple simultaneous hardware failure; do not require networking or storage to be reconfigured; and do not require agents per VM or VM per host.

Below is how we compare on the most important criteria one should be looking for in host side caching software.

Feature Virtunet's VirtuCache PernixData's FVP
Kernel mode software deployed on the hosts being accelerated with both a vCenter plugin and web GUI for management Yes Yes
Operating Systems supported ESXi 5.x, 6.x ESXi 5.x, 6.0 (not 6.5)
Caches hot data from any SAN based storage appliance Yes Yes
Caches reads and writes Yes Yes
In case of write cache, protects data loss if host or SSD fails by replicating writes to one or more SSDs in one or more hosts in the VMware cluster* Yes* Yes*
Continuously syncs write cache from in-host SSD or RAM to backend storage appliance Yes Yes
Signed and certified by VMware Yes Yes
Supports any in-host high speed media – SSD (SATA, SAS, PCIe, NVME) and/or RAM as caching media Yes Yes
Support for third party multi-pathing plugins** Yes** No**

* Differences between Pernix and Virtunet architecture with regards to data protection in case of host/cluster/datacenter failure

Both Pernix and Virtunet cache writes to in-host SSDs without synchronously committing the writes to backend storage appliance. This aspect accelerates writes but also introduces the possibility of data loss in case of host failure, since at any point in time there will be writes on the in-host SSD that are not synced with backend storage. With both PernixData FVP and Virtunet VirtuCache, the VMware cluster can remain operational and there will be no data loss in case a maximum of two hosts fail simultaneously. The reason is that in both software, all writes are simultaneously written to either one or two additional SSDs in one or two additional hosts in the VMware cluster. The number of copies of writes distributed across SSDs and across hosts is an admin configurable option called replication factor. Now if the replication factor was 2x, and if a maximum of two hosts were to crash at the same time, both us and Pernix will immediately sync the backend storage appliance from the mirrored copy of the write cache from a third host. In this respect the functionality between Pernix FVP and VirtuCache is similar. However in case the entire datacenter were to lose power or for some other reason all hosts were to fail at the same time, with PernixData, you will have data loss when the hosts are brought back up, whereas with Virtucache, there will be no data loss in this situation.

** Differences between Pernix and Virtunet in their support for third party multi-pathing plugins

The advantage of VirtuCache over PernixData is that in cases where customers insist on using non VMware multi-pathing plugins (MPP) from storage vendors like Nimble Storage, Dell Equallogic or EMC (Power Path), PernixData will not work. PernixData’s FVP needs to replace these MPPs with VMware Native Multi-path Plugin (NMP).

By default, VirtuCache is also a path selection plugin to VMware NMP, however if the customer insists on keeping their existing storage vendor MPP, Virtunet has an alternate software driver that does not require third party MPPs to be replaced.

As a side note, this article was inspired by an unusually large number of queries we are getting from users of PernixData FVP software who are looking for an alternative. This is most likely because PernixData's FVP platform is being sunset as a result of their getting acquired for less than the money invested in them, in an all too familiar Silicon Valley story line of a heavily funded startup not being able to ramp revenues fast enough despite good tech. On the other hand we are entirely employee owned and profitable. How we run our business and our resulting longevity, which in turn results in long term relationship with our customers, might be a bigger differentiator than technical merit. That thread of VC funded businesses vs. customer funded ones is a topic for another blog post.;-)

A Counter Intuitive Approach to Solve the Peculiar Problems of Video Storage

By not using dedupe, compression, or RAID, using slow HDDs in centralized storage, and moving SSDs to compute hosts, we arrived at low price per capacity and performance for video storage.

Here are unique requirements of video storage, some are obvious and others not so much, that inspired us to put together a different architecture than the conventional storage OEM design.

CEPH Storage is Ideally Suited for Disaster Recovery (DR) Infrastructure

CEPH storage from Virtunet has all the features of traditional iSCSI SAN with the exception that it is reasonably priced because it uses commodity servers with all off-the-shelf hardware. And so it is ideally suited for backup and DR storage which needs to be cheap above all else.

Improving Jenkins Performance

By improving storage performance, Virtucache was able to improve the performance of Jenkins based Continuous Integration process, which in turn resulted in quicker build-test cycles.

Reducing Write Latencies in CEPH Storage

CEPH is a popular open source storage software. However its write latencies are high. VirtuCache caches CEPH volumes to in-host SSDs and by doing so reduces VM level latencies considerably.

Improving Performance of Microsoft Dynamics AX ERP

Microsoft Dynamics AX transaction processing is write intensive and its reporting is read intensive, thus putting pressure on customer's existing storage infrastructure. By caching frequently used data from customer's existing storage to in-host SSDs, VirtuCache was able to reduce read and write latencies for AX running within VMware VMs.

EMC Fast Cache Storage Controller Based Caching for VNX Appliances versus VirtuCache Host Side Caching for Any SAN based Appliance

In case of FastCache or any storage appliance based caching, the SSD is more expensive than if the same SSD were bought retail. Also the SSD performs better in the host than in the storage appliance, since the SSD in the appliance is constrained by the network and controller.


EMC FastCache is SSD based caching functionality sold by EMC for their VNX appliances. It tiers frequently used data, mainly reads, to SSDs in the appliance from slower HDDs on the appliance.


VirtuCache is software sold by Virtunet (and competing with EMC's FastCache) that is installed in the VMware kernel along with a SSD in the same VMware host, and it caches frequently and recently used data, both reads and writes, to the in-host SSD from any SAN based storage appliance.

This blog article lists the differences between VirtuCache and EMC's FastCache.


How to Select SSDs for Host Side Caching for VMware – Type, Model, Size, Source and Raid Level ?

Go with enterprise grade and not consumer grade SSDs. And deploy the SSD behind a good Raid controller (queue depth > 128). Samsung SM863 and Intel S3710 are good choices. The SM863 is better value for money. Also, don't skimp on the Raid controller since you don't want it to choke before the SSD does.

Though this article is in the context of using SSDs with VirtuCache (our Host Side Caching software for VMware that improves the performance of any SAN based storage appliance), these principles apply to the larger category of host side storage software.

This blog article will cover the below topics

- Select SSD type - SATA, SAS, OR PCIe?

- Size the SSD?

- How many SSDs are needed in a VMware Host and across the VMware cluster?

- The need to locally RAID the SSD?

- Where to buy the SSD from?

How To Address Storage Performance Concerns Before Migrating Physical Servers To Virtual

By improving storage performance for VMs, host side caching facilitates P2V of IO intensive bare-metal servers. And it saves capex because there is no storage upgrade involved.

If you have not yet virtualized your physical servers due only to perceived storage performance issues in VMs, then deploying VirtuCache will help. Since VirtuCache caches frequently used reads and all recent writes to in-host SSD and/or in-host RAM, from any back-end storage appliance, the storage performance from within a VM will now be considerably higher than from within your existing physical Linux or Windows server. As a result, P2V of database servers and other storage IO intensive applications is a big use case for VirtuCache.

This blog article talks about how to assure yourself BEFORE you do the P2V that the VirtuCache accelerated storage + VMware infrastructure will perform better than your existing bare-metal servers.

Also a customer use case illustrates that VirtuCache accelerated bare-metal server (when VirtuCache is deployed in bare-metal Linux) performs at the same level as VirtuCache accelerated VMware VM (when VirtuCache is installed in the VMware kernel), thus proving that virtualization in itself does not reduce application performance.

VirtuCache Helped Reduce Storage Capex at a SaaS Provider

VirtuCache accelerates storage appliances to the same extent regardless of whether they have faster SAS hard drives or slower SATA drives, and regardless of the age and speed of SAN. Thus we help postpone a SAN upgrade, or if the customer is looking at a capacity upgrade, selecting an appliance with cheaper SATA hard drives would suffice. We save them capex dollars either way.


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