Tiered Storage: Layers Promise Big Savings


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Storage tiering, the concept of storing various types of data on media with different capacities – like speed, for instance – is a popular technique in today's data centers.

DeepStore provides unusual data storage, and it is a perfect illustration of innovative tiered storage at work.

If you've never heard of DeepStore, that may be because it operates a vast file archive at the bottom of a salt mine. It has almost limitless capacity, and it provides a cool, dry, stable environment where paper documents can be stored for long periods at low cost.

When it comes to digital data, there's also plenty of innovation around tiered storage going on right now. That's because the amount of different ways of storing data is exploding.

In the past, tiered storage was all about moving data between hard disk drives (HDDs) and tape – with different types of HDDs (15k disks, 7.2k disks, SAS drives, SATA drives), different configurations of HDDs (short stroking, data striping and so on) and different implementations of tape (tape libraries, offline archives) providing different tiered storage layers with different cost, performance and capacity characteristics.

New Tiered Storage Layers

But that model based around HDDs and tape has been blown out of the water due to the emergence of a whole new top layer of tiered storage based on solid state drives (SSDs). (Flash can also be used in server and storage system caches too.)

And further down the pile, the cloud has also emerged as the home to one or more new tiered storage layers thanks to the availability of low cost cloud storage resources accessed through cloud gateways, and through ultra-low-cost cloud-based offline archiving services such as Amazon's Glacier or Google Cloud Storage Nearline.

So rather than the traditional four or five layers of tiered storage, (Tier 0 or 1 thru 4) what's now emerging is a tiered storage model with a far higher number of tiers. Each one is subtly nuanced to produce a different combination of three key storage attributes: cost, performance and capacity.

Tiered Storage for Bottom Line Benefits

That's significant for businesses because ultimately tiered storage is not driven by the needs of the IT department: it's an artifact that owes its existence to accountants, due to the contradictory needs of data users and the business as a whole.

For IT departments and the consumers of IT services, the ideal situation would be to store all data at Tier 1 (or Tier 0, if there is one) for the highest possible performance, regardless of cost.

But for a business that aims to maximize profits, or an IT department with a finite storage budget, cost-efficient deployment and use of storage is important.

Given that constraint, the optimum solution is to store data in the lowest-cost layer of tiered storage that provides at least the minimum storage performance (and capacity) required.

In theory then, it follows then that the more storage tiers are available, the more precisely minimum data performance (and capacity) requirements can be met. Less data will be housed in an expensive high tier because the cheaper tier below doesn't offer sufficient performance or capacity.

That's the theory, anyway, but Tony Lock, an analyst at Freeform Dynamics, points out that in practice there's a limit to how many tiers it's useful to have. "Having more tiering options is great as long as there are enough different workloads to make use of those options. Could there be too many tiers? Maybe."

That's because choosing which data to put into a wide choice of tiers may ultimately be the sticking point. "If data classification becomes too complex then you probably will end up not doing it at all," he says.

Software-Defined and Tiered Storage

The concept of tiered storage is not new: manual approaches to tiered storage have been used by storage administrators for years. And automated systems that move data between different storage systems, between different drive types or RAID groups within a single system, or on different storage media on a hybrid storage system are a more recent development that dates back to the 1980s or even earlier. Many storage vendors (and even operating system makers) now offer automated tiering software.

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