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.
VirtuCache is software that improves the performance of Equallogic appliances without requiring you to upgrade the appliance or the SAN network. The performance improvement you will get from your Equallogic appliance will rival an upgrade to an all-flash array.
Equallogic appliances were the workhorses of the enterprise storage market a few years ago. They were cost effective at high capacities. The only drawback was that they are slower since they are primarily hard drive based, and when connected to VMware they exhibit all the 'IO blender' symptoms resulting in high VM level storage latencies.
VirtuCache is installed in VMware vSphere kernel. It then automatically caches frequently and recently used data from any backend storage to any high speed media (RAM/SSD) in the VMware host. By bringing large amounts of 'hot' data closer to the VMware host GPU and CPU, VirtuCache improves the performance of all applications running within VMs including GPU assisted operations.
The biggest difference is that we cache reads and writes, VMware's VFRC caches only reads. Caching writes improves the performance of not only writes, but also of reads, and even in a read dominated workload.1
Then there are other differences as well –
With VFRC, the in-host SSD has to be carved out amongst VMs and capacity manually assigned to each VMDK.2 Such manual assignment of cache capacity on a per VM basis is not required with VirtuCache;
With VFRC, if a host fails or even during manual vmotion, VMs don't migrate unless the target hosts have adequate spare SSD capacity to honor SSD reservations of incoming VMs.4,5 We support VMware HA and DRS without any restrictions;
The biggest reason you might not see performance improvement with VFRC is because it only caches blocks aligned at 4KB boundaries. 7 Most storage IO in Windows and Linux VMs is not aligned;
VMware View or Xendesktop do not support VFRC.6 We do;
In VFRC, SSD failure results in VM failure, because all storage IO is interrupted.3 Not so with VirtuCache.
For a complete list of differences, please review the below table with accompanying cross-references:
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 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.
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.
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.