Budget constraints typically rule out replacing existing storage with a flash-enabled storage system or an all-flash array -- but not always. Next time we'll look at how an ROI can be developed to justify that investment. In the meantime, let's say you have $50,000 to augment your existing storage with SSD. Here are four possible money-saving implementations that we'll also discuss in my upcoming webinar "SSD on a Budget?"
1. SSD Appliances.
A solid-state appliance typically is an all-flash shared storage device that has limited data services. Instead it's usually focused on delivering performance. This lowers costs, but at the expense of a feature-rich array and the increased complexity of managing another silo of storage.
[ Afraid of losing data during cache writes? Read 3 Ways To Protect Cache Writes. ]
Virtualized environments such as VMware help resolve these shortcomings. As I wrote in "Preparing Storage For Increased VM Density," with the right tools you can easily identify sluggish VMs and migrate them to a high-performance SSD. Hypervisors like VMware can also provide much of the data services -- thin provisioning, snapshots and replication -- that these appliances lack.
2. Network Caching Appliances.
Another option similar to SSD appliances is the network caching appliance. As I wrote in "NAS Acceleration Is More Than Just SSD", these devices sit in front of existing SAN or NAS systems and optimize performance by caching hot data to an SSD area on the appliance. In many cases they also optimize network I/O and other operations as well. These devices have the advantage of not requiring manual movement of VMs, but they have the disadvantage of potential cache misses, which SSD appliances do not because the entire VM's image is statically placed on them.
3. Server-Side PCIe Solid-State Devices.
Yet another option is to use PCIe solid-state devices either for virtual memory swap space or for local caching. These devices are ideal if you have a few problematic hosts that can use a performance boost. They're also great if you can't upgrade or optimize the storage network overall because of budget concerns. In these situations PCIe SSDs offer the surgical quick strike that many environments need.
There are problems, though, with PCIe SSDs. First, if you have a dozen hosts with performance problems, this can be an expensive solution. Second, if you're using the device for caching reads or read/writes, VM migration can cause challenges that many caching software solutions are not prepared to manage. Finally, it's more expensive and sometimes more complex to provide PCIe SSD high availability (HA). You'll have to work around all of these issues.
4. Server-Side SSD.
Finally, you have the option of the drive form factor of solid state devices. SSDs provide the same network elimination benefits that PCIe SSD do without the HA complexity. Building a RAID from what are essentially drives is relatively easy. There are no special drivers to load because the operating system recognizes the drives as storage devices. Also, solid state drives are far less expensive than PCIe SSDs.
The apparent shortcoming of SSD when compared to PCIe SSD is the latency of the storage protocol stack and its raw performance. Modern SSDs are closing the gap, though, by increasing their performance and using the latest SAS connectivity.
Which setup is best for you? It depends on your environment and IT capabilities. A shared scenario, such as an SSD appliance or network caching appliance, boosts speed across multiple storage devices and connected hosts. The PCIe or solid state drive scenarios are ideal for helping a few hosts struggling with a performance problem.
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