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Tiered storage model: Five new developments

Tiered storage is enjoying a comeback, a second act, a makeover … you get the point. Until recently, a tiered storage model was simple enough to understand and not that interesting. You

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took some type of storage, and depending on how often and how fast you needed to access it, you made decisions about how and where to store it.

But solid-state storage is getting people excited about storage tiers. Every year, a little more than half of our Storage magazine survey respondents tell us their storage systems are tiered. But these days, 60% of them are doing something new with their tiered storage: They're using flash-based tier-zero storage. And more than half of the survey respondents use an automated process to tier storage to keep the data on that most expensive tier to a minimum. Suddenly a tiered data storage model is worth talking about again. Here are five things you should know about the new look of tiered storage.

1. Hot data and tier zero. There's old tiering and new tiering, and if you are talking about today's new storage tiers you will likely hear about flash solid-state drives (SSDs) storing "hot data" on a temporary basis. This data is written to a flash tier (sometimes called tier zero) for rapid response. However, SearchStorage contributor Jon Toigo said companies should beware of building too many tier-zero and tier-one layers, and remember that some data should be relegated to a cooler tier (tier three or tier four). A recent article of Toigo's on best practices for creating storage tiers spelled out the various vendor approaches to tier zero and hot data.

2. Not everyone needs SSDs for auto-tiering. It's easy to think of automated storage tiers as owing their popularity to the all-flash phenomenon. Several vendors did their part to tie the two together, telling customers the arrival of SSDs in enterprise storage arrays would enable the sort of automated tiering that data storage administrators desperately needed. But Amerijet International is one company that said SSDs didn't give them faster performance on all the applications they write to; however, Compellent's automated tiering software did do the trick with faster spinning drives. Senior News Director Dave Raffo learned the details of Amerijet's auto-tiering project and discovered you don't always need flash to make it work.

3. Vendor approaches vary. So, do you go with flash first, flash pools or flash cache? Do you have a tier four? Depending on which vendor you ask, a tiered storage model can be automated in a variety of ways, from a DRAM cache to a flash cache in the storage controller. Should you start at the bottom with a storage cache or at the top as EMC suggests with its "flash first" approach? Major storage vendors offer different approaches in using flash technology as the foundation for automated storage tiers, and it's important to know their recommendations and rationales, such as hit rates and performance improvement.

4. Caching can compete. In all the excitement about automated storage tiers it might be easy to forget that solid-state storage can also be used as a cache. The end goal is the same: Get the most frequently accessed data on the fastest tier. But SearchStorage expert George Crump reminded readers that the two differ in a significant way. When discussing caching versus tiering, Crump pointed out that automated tiering removes data from the hard drive, while caching creates an additional copy of the hard-drive data. That means failure of a cache would translate to a performance issue, but not a data loss.

5. No more tiers? Try all-flash. If you believe NetApp CEO Tom Georgens, tiering -- even with SSDs helping to make it more popular -- is going out of style. Georgens has been as quoted saying that managing migration of data between Fibre Channel and SATA systems won't be necessary as major vendors roll out all-flash systems. Startups such as Kaminario, Nimbus Data, Pure Storage, Violin Memory and Whiptail have all-flash systems. IBM in April launched Flash System all-flash arrays as part of Big Blue's $1 billion all-flash strategy. In June, Hewlett-Packard joined the all-flash party with a 3PAR StoreServ system designed for SSDs. EMC has its XtremIO all-flash array in limited release, and NetApp plans to add a FlashRay all-flash system this year. Because an all-flash array has one tier, no tiering software is required.


This was first published in June 2013

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