Postpone SAN Upgrade

Postpone SAN Upgrade

Postpone SAN Upgrade

A SAN upgrade to improve storage throughput and latencies involves deploying flash on the SAN and upgrading the storage network by replacing the HBAs on each host and replacing the SAN switch. Such a wholesale replacement of equipment makes SAN upgrades expensive and disruptive.

Deploying VirtuCache with an in-server SSD is a higher performing alternative than a SAN upgrade. This is because of the below reasons:

In a flash based storage appliance, the SSDs are behind the network and storage controller. With VirtuCache, the SSD is on the ESXi host motherboard, hence closer to the CPU that will consume the IO. It is connected to the CPU over a dedicated SAS or SATA bus that is a higher capacity link to the CPU than a shared network in case of a flash based storage appliance.

We distribute caching to each CPU on each ESXi host. As opposed to a storage appliance that processes the caching workload on typically no more than two CPUs (storage controllers) on the appliance. Not only are more CPUs processing caching workload in our case, but each of the CPUs on the ESXi hosts is almost always higher powered than the controller on the storage appliance. This results in higher caching efficiencies (higher cache hit ratio) with our solution compared to storage controller based tiering or caching.

We are a much cheaper alternative as well. Unlike a SAN upgrade we do not require replacing host based NICs (for iSCSI) or Fiber Channel HBAs, and the SAN switch. Also commodity SSDs installed in the ESXi hosts are an order of magnitude cheaper than storage vendor provided SSDs for similar performance profile.

So by complementing existing older storage appliances with server side VirtuCache and server side SSDs, much lower latencies and higher throughput can be achieved, sparing the customer the cost and pain of a wholesale SAN upgrade.

Postponing a SAN Upgrade for Software-as-a-Service Business Unit at Computer Associates

Computer Associates is a Fortune 500 company in the business of IT management software. Over the past few years, they have focused on promoting a subscription based SaaS model for all their software solutions that were previously deployed on-premise only. Such a shift in deployment model required setting up a large scale server, network, and storage infrastructure.

On the storage side, Virtunet was provided the opportunity to compete for CA’s business that called for improving the IOPS and reducing the latencies from their existing disk based storage appliances.

Server and Storage Infrastructure at Computer Associates SaaS BU

Each cluster of VMware hosts had 20 physical servers connected to EMC’s disk based Clariion appliance on 4 gbps Fiber Channel links. CA had plenty of capacity. However they needed to ensure low latencies even during sudden spikes in workload.

Listed below were the three choices available to CA

Replace their existing storage appliance with EMC VNX 7500 hybrid (disk + SSD) appliance.
Replace their existing appliance with Violin Memory’s all-Flash appliance.

Both these above options also meant upgrading from 4gbps FC to 16 gbps SAN switch and HBAs for each of the 20 hosts.

Or, augment their existing storage infrastructure with VirtuCache. This option would let them keep their existing disk based storage appliance and storage networking infrastructure.

Cost Comparison between Hybrid Appliance, All-Flash Array and VirtuCache

From publicly available data, a single EMC VNX 7500 with 60TB of 15K RPM disk, 1.5TB of flash, and 96 GB RAM, that CA was looking at costs $330,000. This hardware does 36,000 IOPS.

A Violin Memory all-flash array costs $800,000 for 60TB and does 900,000 IOPS.

Add to this the cost of a 48 port Brocade 65XX FC switch at $40,000, and newer FC HBAs at $1500/HBA.

Now compare this with costs for in-server SATA SSD with VirtuCache. A single 800 GB SATA SSD with VirtuCache costs about $3,000. Such a SSD does 100,000 IOPS

The below table breaks out the costs on a per GB and per IOPS basis

Storage Type Dollar per GB Latencies Dollar per IOPS Entry Cost
Violin Memory All-Flash Array $15 Network Dependent $1 $900,000 including networking upgrade
EMC VNX 7500 $7 Network Dependent $10 $400,000 including networking upgrade
VirtuCache with SATA SSD $4 Less than 5 millisecond from the VM 3 cents $3000 for one ESXi host.

CA could deploy our solution in phases starting with a few ESXi hosts that had the most storage IO issues. With a SAN upgrade CA had to commit to the budget for the entire SAN upgrade upfront and they would’ve had to rollout the SAN upgrade across the entire site at once, thus making the SAN upgrade disruptive and expensive.

Benefit to CA

Using in-server SSDs with VirtuCache to accelerate SAN I/O is a higher throughput and lower cost solution than a traditional SAN upgrade. Deploying VirtuCache is also non disruptive to storage operations. VMware administrators at CA were able to install VirtuCache and SSDs on their ESXi hosts in under 20 minutes per host, and within a few minutes of the deployment, they started seeing performance gains.


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