When it comes to making virtual server farms easier to manage, the SAN is the great enabler. But when it comes to maximizing virtual server performance, the SAN is the great bottleneck. A single host running dozens of virtual machines (or more) can easily generate enough I/O operations to reduce overall SAN response time, increasing I/O latency and adversely affecting virtual machine performance. Adding more spindles may help in the short term, but that can be very disruptive to the storage infrastructure and does not really take care of the root of the problem: I/O bottlenecks.
One company that is working to improve VM performance by reducing storage I/O latency is PernixData. PernixData FVP is an add-on module for the VMware vSphere hypervisor that creates a cluster of high-speed SSD devices across multiple vSphere hosts. The PernixData "flash cluster" creates a distributed cache for reads and writes to the SAN, accelerating virtual machine I/O without requiring any changes to the VMs or their host datastores. And because the flash cluster is shared among hosts, PernixData FVP fully supports VMware services such as vMotion, DRS, and HA. VMs can continue to move freely from host to host without incurring a cache "miss" penalty.
By consolidating server-side flash into a single shared flash cluster, PernixData FVP leverages many small flash investments into a large I/O improvement. Installation is quick and easy, and it doesn't even require a reboot of the hosts. PernixData FVP comes in SMB and Standard versions. The SMB version is $9,999 for up to four hosts and 100 VMs. The standard edition is $7,500 per host with no restrictions on the number of hosts or virtual machines.
Zero to hero
Here is the quick takeaway for PernixData FVP: zero changes to the virtual machine environment. There are no changes to the VMs or to the underlying host datastores, and PernixData FVP is transparent to both the VMs and the SAN.
PernixData FVP works with vSphere 5.0 and vSphere 5.1 hosts. It installs into the vSphere kernel via the VMware update utility and accelerates I/O requests between VMs and the SAN. Configuration consists of creating the flash cluster and adding the server-side flash devices to the cluster. You then designate the datastore to be accelerated. This is a bulk operation — you do it once for the entire VM datastore on the SAN, not for each VM. The VMs residing in the datastore will automatically inherit the attributes of the FVP flash cluster, as will any VMs added to the datastore later. Alternatively, you can add individual VMs to the flash cluster so that only the I/O of chosen VMs is accelerated.
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