Storage Caching vs Tiering Part 1

Recently I had the privilege of being a Tech Field Day Delegate. Tech Field Day is organized by Gestalt IT. If you want more detail on Tech Field Day visit right here. In interest of full disclosure the vendors we visit sponsor the event. The delegates are under no obligation to review good or bad the sponsoring companies.

The first place hosting the delegates was NetApp. I basically have worked with several different storage vendors but I must admit I have never experienced NetApp in any way before. Except for Storage vMotioning Virtual Machines from an old NetApp (I don’t even know the model) to a new SAN.

Among the 4 hours of slide shows I learned a ton. One great topic is Storage Caching vs Tiering. Some of the delegates have already blogged about the sessions here and here.

So I am going to give my super quick summary of Caching as I understood it from the NetApp session. Followed by a post about Tiering as I learned from one of our subsequent sessions from Avere.

  1. Caching is superior to Tiering because Tiering requires too much management.
  2. Caching outperforms tiering.
  3. Tiering drives cost up.

The NetApp method is to use really quick Flash Memory to speed up the performance of the SAN. Their software attempts to predict what data will be read and keep that data available in the cache. This “front-ends” a giant pool of SATA drives. The cache cards provide the performance the the SATA drives provide a single large pool to manage. With a simplified management model and using just one type of big disk the cost is driven down.

My Take Away in Tierless-Caching

This is a solution that has a place and would work well for many situations. This is not the only solution. All in all the presentation was very good. The comparisons against tiering were really setup against a “straw-man”. A multi-device tiered solution requiring manual management off all the different storage tiers is of course a really hard solution. It could cost more to obtain and could be more expensive to manage. I asked about fully virtual automated tiering solutions. Solutions that manage your “tiers” as one big pool. These solutions would seem to solve the problem of managing tiers of disks, keeping the cost down. The question was somewhat deflected because these solutions will move data on a schedule. “How can I know when to move my data up to the top tier?” was the question posed by NetApp. Of course this is not exactly how a fully-automated tiering SAN works, but is a valid concern.

My Questions for the Smartguys:

  1. How can the NetApp caching software choices be better/worse than software that makes tiering decisions from companies that have done this for several years?
  2. If tiering is so bad, why does Compellent’s stock continue to rise in anticipation of an acquisition from someone big?
  3. Would I really want to pay NetApp sized money to send my backups to a NetApp pool of SATA disks? Would I be better off with a more affordable SATA solution for Backup to Disk even if I have to spend slightly more time managing the device?
Written on November 19, 2010