Posts by Barry Burke

EMC has been shipping VAAI since 2010

VAAI support has been available for all VMAX and CLARiiON arrays since last year, and is also standard for the new VNX arrays.

But it's not quite that simple

Without getting into the interface battles (PCI vs. FC/SAS/IB/etc), consider a few things:

PCI/x (et al) is limited in the number of devices it can support and the distances they can be from one another, while FC (et al) are far easier to extend over distance and can support far more addressable devices.

Performance-sensitive datasets frequently exceed the size of even a few disk drives. Given the cost of NAND in the short term, the most economical use could well be as an L3 cache instead of a tier 0, at least for some applications.

There are scarce few applications whose access density is hundreds of thousands of IOPS against a few hundred GB of data - more typically high-IOP applications require far more storage capacity (if they didn't, they'd just load it all into SDRAM).

As dynamic cache, NAND isn't significantly more dense than DDRx SDRAM, while it is significantly slower (particularly for writes). And while cheaper per GB, the $ IO/response time is that different from SDRAM either.

The default I/O size for most database engines is 8KBytes - locality of reference studies show that 8K is better than 4K for caching (yeou basically get the extra 4K for "free"). Other studies have shown that modern databases perform better with 128KB read granularity. Smaller isn't necessarily better, unless you're truly operating at memory buss speeds - NAND is too slow for that.

As permanent storage, NAND needs added layers of data integrity protection, and not just within the device itself - mirroring or RAID is required to protect against the inevitable device failure. This adds a not insignificant amount of performance-sapping overhead - it is doubtful that the Quicksilver configuration would have come anywhere close to 1M IOPS had error detection, correction and prevention been included.

Although counter-intuitive, customers frequently find that applications perform better with external SDRAM SSDs and even large-cached storage arrays than they do with internal caches OF THE SAME SIZE - there's a significant advantage in cache algorithms that are disk-aware (seek & rotational positioning, etc.)

And the most important consideration is this - the folks arguing for "in the server" either build servers or build PCI-bus products; the ones arguing for "in the storage" build arrays or drive-form-factor devices. But both servers and storage today use SDRAM and spinning rust - there's no reason that NAND (or any other technology) has to be an Either-Or discussion.

The reality will be both will thrive, and most likely within the same I/O path. The debate is truly pointless!

- the storage anarchist

Complimentary solutions

That should be Sun AND EMC - there's no reason for these to be thought of as competitive alternatives...except that EMC is shipping Flash drives already, while Sun has made more of a statement of direction.

A cached disk array already delivers I/O to servers much, much faster than disk drives alone can - and thus servers have already been "optimized" for faster-than-disk (and even faster-than-flash) I/O performance when dealing with SAN-based storage. And since RAM is still so much faster than NAND FLash, cached arrays still add significant benefit to I/O performance even for Flash-based storage.

As to how the inherent characteristics of NAND Flash are handled in the devices EMC is offering today, I've covered much of this in my blog:

http://thestorageanarchist.typepad.com/weblog/2008/01/0059-bold-fast.html

Net-net: customers and applications simply treat the devices as they would any SAN-based disk storage - all the management is handled within the drive and with the cooperation/assistance of the storage operating system. NBD.

Unfortunately, as I pointed out in my blog yesterday none of the other vendors have come forward to explain their approaches yet.

http://thestorageanarchist.typepad.com/weblog/2008/06/1010-sun-adds-c.html

They have no choice but to address these characteristics, but they've been mum on the details so far...