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PCIe flashers bash storage networks

They slow you down, man

GElsinger and Lightning PCIe card at Oracle OpenWorld

Blocks & Files A sea change in storage industry thinking is occurring: storage networks are now seen as slowing down access to data. The PCIe flash DAS hare beats SAN and NAS tortoises every day of the week.

We can call PCIe flash "storage memory" if we wish, but it's basically very fast direct-access storage, a closely-coupled data bucket. Who cares whether we call it a new form of memory? The main thing is: it gives applications in servers much faster access to stored data than if it was stored on networked disk.

A disk can do 250 or so IOPS. Flash can do hundreds of thousands of IOPS. That's it, game over, Flash DAS rules, okay! But this overarching message obscures networked storage's advantages where many servers need to share data (NAS) or a large storage resource (SAN).

The networked storage problem, when compared to flash DAS, is twofold: disks have seek time latency as well as low IOPS rates, and the network adds its own latency to compound things. Solid state drives (SSDs) in a networked array have the same network latency problem, although they have the IOPS rate advantage over disk.

In truth network latency is not the evil ogre in networked storage access; the real (twin) ogres are disk seek times and low IOPS numbers. In sequential I/O, disks are plenty fast, but in today's world IOPS seem to be rated more highly than MB/sec.

Virtualised multi-core, multi-threaded servers are impatient. They want data for the apps in their virtual machine instantly. It's odd; now that CPU cycles are cheaper than ever before, they are treated as the most precious resource in the data centre.

It is all about time and cloud computing and centralisation of application software. We are turning servers into the computing equivalent of drag racers and the fuel (data) feeds to their engines are being tuned and tweaked to pour data into them faster than ever before. As car engines moved from carburettors to direct fuel injection so servers running random I/O-bound apps are moving from storage networks to PCIe flash.

Downstream the focus is moving to networked storage arrays, now becoming flash-enhanced storage arrays and even all-flash storage arrays, getting better at serving PCIe flash. Here too, network latency may well become the villain of the piece, prompting general moves to 16Gbit/s Fibre Channel and 40Gbit/s Ethernet.

Whatever delays data access is evil, that's current storage thinking – and PCIe flash is the storage industry's Great New Hope. But for how long? ®

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