The Virtunet DifferenceThe customer selected VirtuCache because:
August 22, 2021; Connecticut, USA.
Foxwoods Casino and Resorts operates six casinos and a couple of 2200 room hotels in Ledyard, Connecticut.
They used VirtuCache to improve the write performance of EMC VNX appliance.
Foxwood’s EMC VNX appliances already had the FastCache SSD caching functionality from EMC. EMC’s FastCache cached data on HDDs in the VNX to SSDs in the VNX. However FastCache only cached reads and not writes. VirtuCache overcame this shortcoming of EMC VNX by caching all reads and writes to in-VMware host NVME SSD and RAM.
EMC VNX’s FastCache SSD caching functionality has four shortcomings:
- Even the high-end VNX 7500 can accommodate only 2TB of SSDs per appliance
- FastCache doesn’t cache writes, hence writes are not accelerated
- FastCache uses SAS SSDs which are slower than the highest throughput NVME SSDs and RAM
- Lastly, FastCache is expensive.
VirtuCache is a better option than FastCache for the below reasons.
VirtuCache is installed in the VMware physical server. It then automatically caches all reads and writes from/to any SAN based storage appliance to host RAM and/or in-host SSD. Consequently, VirtuCache improves storage performance from our customer’s existing storage appliance, thus allowing higher hardware consolidation ratios, and improving performance of applications (that are installed in VMs).
Below is a table comparing these two options.
|EMC FastCache SSDs in the VNX appliance||Virtunet VirtuCache caching from VNX to in-host SSD/RAM|
Higher latency because
• SSDs behind controller and shared network.
• Only 2/4 Controllers (CPUs) involved in caching.
• Uses SAS SSDs only.
Lower latency because
• Cache media closer to CPU, there is no network overhead.
• Each VMware host CPU involved in caching. Hence more CPU used in caching.
• Can cache to any media installed inside the host including really fast NVME drives and even faster RAM.
|Accelerates frequently used reads and reads that are changed in memory.||Accelerates all reads and writes.|
|Caching granularity is 64KB block size, meaning that even if the application retrieves data in smaller chunks, FastCache will allocate 64KB space for this data.||VirtuCache caches data at the granularity of data requested. Hence space on the SSD is used optimally. This results in higher cache hit ratio with VirtuCache.|
|Maximum SSD that can be installed in a VNX is only 100GB in VNX 5100, 500GB in VNX 5300, 1TB in VNX 5500, 1.5TB in VNX 5700, and 2.1TB in VNX 7500.||Maximum SSD that can be used in VirtuCache is 8TB per Host, considerably more than VNX.|
|Expensive – SSDs in VNX cost $12/GB.||Affordable – The same SSDs that go in the VNX if bought retail costs $0.30/GB. If you choose to go with higher performing NVME SSDs, those too go for 30 cents/GB.|
Cost and performance comparison between VirtuCache and EMC VNX FastCache
The VMware administrator at Foxwood Casinos bought VirtuCache for their 4-host cluster to complement FastCache. VirtuCache improved the write performance for their applications by caching to a combination of 3.2TB Samsung PM1725b NVME SSD and 128GB RAM in each host. The cost for VirtuCache, NVME SSD, and RAM worked out to $5,500 per host ($3600 for VirtuCache, $900 for 3.2TB NVME SSD, and $1000 for 128GB RAM). So the total cost for 4 hosts was $22,000. The maximum IOPS and throughput this combination provided was around 2 million IOPS (64gbps throughput) across the 4 host cluster. This price was comparable to EMC VNX FastCache but the EMC FastCache was only a quarter of the peak IOPS/ throughput of VirtuCache, more so the FastCache performance boost was only for reads. It didn’t accelerate writes at all. Since the customer had already bought FastCache and there was no option to return it, they decided to use both VirtuCache and FastCache.
Now if you are planning to buy EMC VNX, we recommend that you buy it without FastCache and rely only on VirtuCache (along with NVME/RAM) for storage performance purposes. In summary, we recommend that you use the backend storage appliance to service capacity aspects of storage and frontend VirtuCache in each ESXi host to service the performance aspects of storage. This will give you the highest IOPS for the lowest cost.