How much disruptive innovation does your flash storage rig really need?

Random IO? Or just plain random?

To have and have not

All the mainstream drive array vendors are singing from this hymn sheet, but equally they are all adopting all-flash array technology and a clear-cut divide is opening up between the ones with standalone all-flash array technology and the ones without.

Dell, HDS and HP do not have separate all-flash arrays that stand alongside their existing arrays. Instead their flash storage is inside these arrays and hence inherits the data protection and management benefits that these arrays already have.

The latest HDS VSP G1000 array, in all-flash mode, is the fifth-fastest performer on the industry-standard SPECsfs2008 NFS benchmark, designed to test storage array's responsiveness to random file IO in a business context.


HDS VSP G1000 SPECsfs2008 NFS benchmark ranking

There are no equivalent benchmark results for new all flash arrays from suppliers such as Pure Storage or SolidFire.

As a rule of thumb we could say a flash-transformed array and software could match many all-flash arrays in pure performance, with the benefit of fitting in to current data and array management processes and the disadvantage of being more expensive to acquire, power, cool and house in a data centre.

Jay Kid, NetApp's chief technology officer, thinks that all-flash arrays outside of legacy storage arrays have their place. He believes that extending the capabilities of NetApp's ONTAP storage controller software would be a stretch too far to cover flash, as its primary focus is disk.

The company's coming all-flash FlashRay and existing EF540/550 systems, neither of which run ONTAP, can run and use flash better than ONTAP.

He says NetApp is excited about FlashRay, a fresh design. It will be "a great $/GB offering, with MLC flash and hundreds of thousands of IOPS."

That is one of the vital aspects. New all-flash arrays deliver more IO operations per second, many more than an existing disk-based storage array architecture can do with the same amount of flash storage and at a much lower cost per IO.

This is true for random IO, the kind that sends disk read-write heads in time-consuming skips across the platters. It is not so true for sequential I/O, where both flash and disk pour data into and out of an array at roughly comparable speeds.

Suits you, sir

Therefore new all-flash arrays are thought to be a good fit for applications needing lots of random IO – ones that are, in the jargon, latency-sensitive, such as databases, real-time analytics and trading software.

The idea is that an all-flash array can satisfy random IO requests from a much smaller data-centre footprint as measured in rack enclosure sizes and therefore needs less power and cooling, as well as less space, all helping to lower its total cost.

Note that array vendors without a new all-flash array in their product arsenal will disagree with this blanket statement.

Dell, HDS and HP, for example, would assert that their flash-transformed traditional arrays are as good as new all-flash arrays and have their existing storage management and data protection features. That means no new storage silo to acquire and operate and no new supplier relationship to manage.

We can build up the characteristics of the ideal application for (1) new all-flash arrays, (2) flash-transformed traditional arrays, (3) flash-enhanced traditional arrays with SSDs and flash caches and (4) all-disk storage arrays.

  • New all-flash array: the most latency-sensitive applications where random IO speed is more important than considerations of a good fit into existing array operation, management and protection processes. Useful in financial and online trading, online transaction processing, data logging, real-time analysis.
  • Flash-transformed legacy storage array (Dell, HDS, HP): as above, according to these vendors, and it may well be that an internal pilot and comparison exercise reveals this to be the case.
  • Flash-enhanced traditional array: for mixed latency-sensitive and less speed-dependent applications such as financial and online trading, online transaction processing, data logging, real-time analysis and near-line data applications, email, office document editing. Fitting in with existing array operational and data management and protection processes is important.
  • All-disk traditional array: least latency-sensitive IO, possibly with a sequential IO pattern and best fit to legacy array operational and data management and protection processes. For example applications dealing with near-line data, email, office document editing and so forth

These four categories are separated by qualitative differences so businesses and public organisations have to balance their budgets and needs and evaluate their own individual best product fit to requirements.

Over time the new all-flash arrays will get better management and data protection processes and may fit into a supplier's legacy operational and management processes.

As an example EMC's ViPR software abstraction layer can be used to operate and provision traditional-style EMC arrays such as VMAX and VNX and the newer XtremIO all-flash array product.

The conclusion to take away from this discussion is use best of breed when you need speed and a traditional array when operational process fit is your priority. ®

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