The Virtunet Difference
At CA, VirtuCache was compared with EMC’s FastCache controller based caching. Since the PCIe flash card that VirtuCache used was closer to the CPU versus EMC’s FastCache SSDs that were in the storage appliance, VirtuCache was much lower latency than EMC’s FastCache. At $7/GB it was also much than $30/GB for the FastCache module.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.
When it was time for Computer Associates (CA) to upgrade both storage capacity and performance , they decided to put their eggs in two different baskets this time instead of just the one (EMC) that they had done many times before. Traditionally with every upgrade they would get more capacity and performance from their newer EMC appliance. This time around, for upgrading capacity they still went with EMC appliances, but only with cheaper SATA Hard Drives in these appliances instead of the high performing 15K RPM Fiber Channel SAS hard drives. Now for the performance aspects of storage, they deployed VirtuCache to cache from their VNX appliances to SSDs in the VMware hosts.
As a result of this two pronged strategy of upgrading capacity and performance independently, they were benefited by lower $/GB for capacity and lower $/IOPS. Expensive hard drives were no longer required since host based SSDs are so much higher performing than even the highest performing hard drives that it doesn’t matter if one deploys 15K RPM SAS drives or the cheaper 7.2K RPM SATA hard drives in the appliance. Also $/IOPS was cheaper compared to EMC Fast Cache SSDs because host side SSDs bought retail or from the server OEM are much cheaper than the same SSDs bought from EMC or any other storage vendor.
Main Challenges
Computer Associates (CA) is the market leading vendor in System Management Software for Enterprise IT.
CA was transitioning their existing on-premise software solutions to a Software-as-a-Service model. In support of this project, CA’s SaaS BU was looking to upgrade their storage capacity and performance to meet the growing demands of their enterprise customers. Since the SaaS operation was a lower cost pay-as-you go model for CA’s customers and also due to increasing competition in the cloud based System Management space, CA was looking to drastically reduce their capital expenditure. And so CA was looking for an alternative to a wholesale storage network and appliance upgrade that they had done many times before.
Server and Storage Infrastructure
CA had Dell R720s servers running VMware 5.1. These servers were connected to 8 gbps EMC VNX 7500s.
VirtuCache Deployment
VirtuCache was deployed on each of the servers in a 16 host cluster. Each such cluster was sharing 120 TB of storage space from two hard disk based EMC VNX 7500s. Approximately 7-8TB of storage capacity was used by all the VMs on each VMware host.
As a standard practice, we recommend that 15-20% of LUN capacity used by each host be the size of the SSD used as a cache device in each ESXi host. As a result CA bought 1TB PCIe flash cards from Fusion IO to be the cache device for VirtuCache. VirtuCache was configured to cache data from LUNs on the EMC VNX 7500 to the 1TB Fusion IO flash card. By serving up more and more IO from the in-server PCIe flash, storage throughput was much improved and latencies much reduced.
Cost Comparison between VirtuCache and EMC VNX 7500
As of 2014, publicly available pricing for an EMC 7500 with 60TB of 15K RPM SAS hard drives, 1.5TB of Fast Cache SSD, and 96GB RAM is $350K. This appliance does 36,000 IOPS. So the cost per IOPS is about $10. Cost per GB of storage is $6. This cost does not take into account the cost of the SAN switch and the HBAs.
Cost for the just the 1.5TB EMC FastCache SSDs was around $45,000. So cost per GB of SSD is $30.
Now let us compare this with costs for VirtuCache and an in-server Fusion IO PCIe flash card. A 1TB Fusion IO Iodrive2 PCIe flash card with VirtuCache costs about $10,000. Such a card conservatively does 250,000 IOPS . So the cost for our solution is $10 per GB of PCIe SSDs. However, it is ensuring low latencies even at high IOPS where VirtuCache provides the most benefit Cost per IOPS with us worked out to 4 cents.
| Storage Type | Dollar per GB | Dollar per IOPS |
|---|---|---|
| Cost for the entire EMC VNX 7500 storage appliance | $6 | $ 10 |
| VirtuCache with FusionIO PCIe card | $10 | 4 cents |
| EMC FastCache SSDs for Storage Controller base Caching | $ 30 | $ 2 |
Benefit to CA
Using in-server flash to accelerate SAN I/O was a higher throughput and lower cost solution for CA than having EMC service both their IOPS and capacity needs from the back-end VNX.