The simplest case is to use an internal SSD either as a drive or a PCIe card inside of a server. Several RAID controller manufacturers have added the ability to support an SSD drive to act as a cache in front of the drives attached to the RAID controller. For the cost of a single SSD drive, or two for redundancy, we've seen dramatic improvements in performance. The SAN can also benefit from cache and the solution does not necessarily have to come from your storage vendor. Several storage virtualization products have the capability to set aside several SSD drives as caching area for reads and in some cases even writes, to existing storage arrays. There are also a few products that are essentially caching switches, and don't require a storage virtualization engine. As is the case with the server example, this can greatly improve performance.
The above two examples cover the block world but NAS systems do not need to be left out. There are several devices that can be placed in front of NAS systems to cache CIFS and NFS traffic as it goes across the network. While many assume that the network is the bottleneck in high performance NAS environments, the thrashing of disk I/O is sometimes the root of the problem; caching should help alleviate that.
Most cache systems are temporal in nature. Meaning that they only hold a unique copy of data for a very short period of time, typically measured in seconds. In fact read only caches never hold a unique copy of data. We are seeing caching devices that are less temporal in nature, meaning they will store a unique copy of data for a longer period of time, maybe minutes or even hours. This is a very interesting development in storage and as we discuss in our article, Architecting Storage Networks for Data Delivery vs. Data Services, has the potential to relegate the current name brand NAS players to deliverers of software components further commoditizing mechanical storage systems.
Probably the more obvious payoff of using SSD as a large cache is helping to fix a performance problem more cost effectively than adding more mechanical drives or replacing those drives with faster drives. Less obvious is using these solutions on an initial purchase, they could very easily allow you to buy a mid-range SAN or NAS instead of a more expensive high end system.
Track us on Twitter: http://twitter.com/storageswiss
Subscribe to our RSS feed.
George Crump is lead analyst of Storage Switzerland, an IT analyst firm focused on the storage and virtualization segments. Find Storage Switzerland's disclosure statement here.
