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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.

This article is the first in a series of two articles that compares our software versus PernixData FVP. The second article compares (with screenshots) GUI and configuration steps for PernixData FVP and us.

Below is how we compare on important criteria.

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 caching, prevents data loss if a maximum of 2 hosts fail, because caching software replicates writes to caching media in at least one more host (and a maximum of 2 hosts) in the VMware cluster* Yes. In addition we protect against data loss in an all hosts down situation.* Yes. Though with FVP, you will lose data if all hosts in the cluster fail simultaneously.*
Continuously syncs write cache from in-host Flash 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. You can cache to RAM, Flash, or a mix of both in varying combinations on different hosts in the same cluster. Yes, though FVP supports either RAM or Flash, but not a mix of both.
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 caching media (in-VMware host RAM and/or Flash) 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 caching media 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 caching media in one or two additional hosts in the VMware cluster. The number of copies of writes distributed across hosts is an admin configurable option called replication factor. Now if the replication factor was 2, 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 peer hosts. 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, if you are using non-volatile Flash (not RAM) for caching, 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 a 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.;-)