Further, working in concert with the automated storage tiering features, the controllers understand which storage blocks are experiencing the most turnover. The controllers move these "hot" blocks to and from the fastest storage, ensuring that the data needing faster access will not wind up on a slower array, but will be prioritized on the set of SSDs, should they be available. This capability is also available with traditional disks, but the inclusion of the SSDs -- specifically, the hybrid 6100XVS coupled with the lower-cost PS4100E -- really shows off the benefits of these features in production workloads.
Let's envision a fairly traditional storage workload for a medium-size infrastructure. We have a bunch of hypervisors driving several hundred VMs, along with general-purpose file sharing, and a passel of databases that drive a Web application tier to provide critical line-of-business applications.
It's common to satisfy all of these storage requirements through the same homogenous storage array, but there are drawbacks. For instance, it means that the long-forgotten, never-again-to-be-accessed 2GB movie file that a user once stored in his home directory will sit right next to the bits that the core database servers are constantly reading and writing. In a perfect world, these files wouldn't mix, but we all know that the world we inhabit is rife with similar examples.
With automated tiering, that neglected movie file will eventually wind up on the slowest disks in the data center, while the database volume will wind up on the fastest -- without any administrative intervention required.
In practice, this process is as simple as setting up the disparate arrays in the same group and introducing the workload. As the controllers get an idea of which data is flowing where, they will automatically distribute the blocks throughout the arrays according to the demand.
In our example, this would mean that the database volumes and high-transaction VMs would wind up on the SSDs, while the movie file winds up on the SATA drives. As the load changes, the solution automatically adapts. If the user shared a link to that movie with the entire company and the movie began streaming to a few hundred people, the controllers would migrate it to faster storage. Thankfully, the Dell EqualLogic SAN HQ software provides the controls to ensure that an odd workload change such as this does not bump more critical data sets from the fastest disk.