Solid State Stor­age: On the road to data cen­ter dom­i­na­tion

On the road to data cen­ter dom­i­na­tion

InformationWeek - - Contents - BY KURT MARKO

SSDs are dis­plac­ing hard drives at a rapid clip in the data cen­ter, as en­ter­prises and cloud providers find them an in­creas­ingly at­trac­tive low-power, faster stor­age op­tion

SSDs are dis­plac­ing hard drives at a rapid clip in the data cen­ter, as en­ter­prises and cloud providers find them an in­creas­ingly at­trac­tive low-power, faster stor­age op­tion

Solid-state stor­age is march­ing through the data cen­ter, dis­plac­ing disks in ev­ery­thing from servers to stand­alone stor­age ar­rays. The rea­sons are clear: sig­nif­i­cantly lower power, faster ac­cess times — par­tic­u­larly for reads — and most im­por­tantly, price points that make SSDs both tech­ni­cally fea­si­ble and fis­cally prefer­able al­ter­na­tive to me­chan­i­cal disks for more and more ap­pli­ca­tions.

SSDs are cer­tainly be­com­ing more com­mon in en­ter­prise data cen­ters, ac­cord­ing to In­for­ma­tion­Week’s 2014 State of En­ter­prise Stor­age Sur­vey. The sur­vey showed 40 per­cent of sur­vey re­spon­dents us­ing SSDs in disk ar­rays, up eight points from last year, while 39 per­cent now de­ploy SSDs in servers, up 10 points from last year. De­ploy­ments are still broad, but not deep, as nearly two-thirds of sur­vey re­spon­dents out­fit 20 per­cent or fewer of their servers with SSDs, and just 48 per­cent have SSDs in more than 20 per­cent of their stor­age ar­rays.

While en­ter­prise SSD use is clearly on the rise, the big driver of SSD adop­tion is cloud ser­vice providers (CSPs) like Ap­ple, Face­book, Google and Mi­crosoft us­ing SSDs in ways few in the in­dus­try would have pre­dicted. Early solid-state de­ploy­ments fo­cused on high- end, trans­ac­tion-heavy ap­pli­ca­tions where their I/O through­put meant one or two SSDs could re­place a shelf full of ex­pen­sive 15K rpm SAS HDDs. To­day, rapid price ero­sion — par­tic­u­larly for con­sumer-grade flash mem­ory — means CSPs are now turn­ing to SSDs for bulk data stor­age and caching — what Kevin Di­belius, Di­rec­tor of En­ter­prise Stor­age at Mi­cron, calls “read of­ten, write few” ap­pli­ca­tions.

Read- dom­i­nant ap­pli­ca­tions are a good fit for cheaper con­sumer-grade drives since they don’t ex­ac­er­bate the most sig­nif­i­cant short­com­ing of NAND flash de­vices: dura­bil­ity. As Nim­ble Stor­age Mar­ket­ing VP Rad­hika Kr­ish­nan points out, there’s an in­her­ent trade­off be­tween flash ca­pac­ity and re­li­a­bil­ity. Higher den­sity is achieved us­ing tighter process ge­ome­tries, multi-level mem­ory cells and less er­ror cor­rec­tion data, all of which make the de­vice less durable and re­li­able. This doesn’t bother CSPs since they are in­creas­ingly us­ing flash for cold, archival stor­age on

highly re­dun­dant and dis­trib­uted file sys­tems, where a drive or even sys­tem fail­ure isn’t cat­a­strophic.

The re­sult is a dra­matic change in flash re­quire­ments. In the past, when high IOPs, trans­ac­tion- ori­ented work­loads were the pre­dom­i­nant SSD ap­pli­ca­tion, de­vices were typ­i­cally spec­i­fied to achieve 10 drive fills per day for 5 years, Di­belius said. That’s 10 com­plete writes of ev­ery mem­ory cell, ev­ery day for five years or al­most 20,000 write cy­cles. To­day, cus­tomers of­ten need prod­ucts only good for one-fill per day, or less — specs that are in line with con­sumer- grade MLC drives, he said. In­deed, he said MLC is ap­pro­pri­ate for about 90 per­cent of Mi­cron’s new cus­tomer in­quiries.

In fact, Di­belius notes that some CSPs have even asked to buy off­spec NAND chips, i.e., those that have failed Mi­cron’s QA test­ing, so they can roll their own flash mem­ory stor­age sys­tems at an even cheaper price. They can do this be­cause their cloud in­fra­struc­ture is suf­fi­ciently re­dun­dant that a high level of drive fail­ures doesn’t com­pro­mise data in­tegrity. Al­though Mi­cron hasn’t yet sold any of these test­ing room re­jects out of con­cern over the long-term cus­tomer sup­port im­pli­ca­tions, it’s clear that for some flash buy­ers, price and ca­pac­ity is far more im­por­tant than per­for­mance, re­li­a­bil­ity and write en­durance.

Even with MLC SSDs crash­ing through the USD 1/GB bar­rier, there’s still quite a price and ca­pac­ity gap be­tween flash and hard disks. How­ever, some flash ad­vo­cates, such as John Scara­muzzo, SVP and GM of SanDisk’s en­ter­prise group, ar­gue that the rate of solid-state mem­ory tech­nol­ogy evo­lu­tion has so far sur­passed that of mag­netic hard disks that the gap is rapidly clos­ing. HDD man­u­fac­tur­ers re­sort­ing to in­creas­ingly ab­struse and ex­pen­sive tech­niques like shin­gled mag­netic record­ing and he­lium-filled drives il­lus­trate Scara­muzzo’s point that HDDs “are run­ning out of gas.”

Mean­while, NAND flash tech­nol­ogy marches on. Scara­muzzo pre­dicts 4 and 8 TB drives by year end and 16 TB next year. Di­belius sets the bar even higher, claim­ing that Mi­cron’s new 16 nm process tech­nol­ogy and 16- die stacks should al­low the com­pany to achieve ca­pac­i­ties of 25 TB be­fore need­ing to move onto the next so- called one-y (sub-16 nm) tech­nol­ogy in a year or two. Of course, these will be MLC de­vices, but the up­shot is that more and more bulk stor­age ap­pli­ca­tions will be­come fea­si­ble and ac­tu­ally prefer­able to run on flash sys­tems.

In the near-term, hy­brid flashHDD sys­tems like those from Avere Sys­tems, Nim­ble, Tegile and most of the ma­jor stor­age ven­dors can deliver all-flash per­for­mance with hard- disk eco­nom­ics. They do this by dy­nam­i­cally ad­just­ing the size of solid state caches and stor­age par­ti­tions in ways that are trans­par­ent and nondis­rup­tive to ap­pli­ca­tions.

Much like flash has grad­u­ally dis­placed hard disks for most con­sumer de­vices, it is march­ing through the data cen­ter and tak­ing up a grow­ing slice of the stor­age pie. Al­though still a rel­a­tively small share of to­tal stor­age, the emer­gence of flash as a vi­able bulk cold stor­age medium for CSPs cou­pled with the rapid pace of tech­nol­ogy im­prove­ment, means that pre­dom­i­nantly all-flash data cen­ters will be a re­al­ity for many or­ga­ni­za­tions within this decade.

The big driver of SSD adop­tion is cloud ser­vice providers like Ap­ple, Face­book, Google and Mi­crosoft us­ing SSDs in ways few in the in­dus­try would have pre­dicted

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