Inside System Storage -- by Tony Pearson

Tony Pearson Tony Pearson is a Master Inventor and Senior IT Specialist for the IBM System Storage product line at the IBM Executive Briefing Center in Tucson Arizona, and featured contributor to IBM's developerWorks. In 2011, Tony celebrated his 25th year anniversary with IBM Storage on the same day as the IBM's Centennial. He is author of the Inside System Storage series of books. This blog is for the open exchange of ideas relating to storage and storage networking hardware, software and services. You can also follow him on Twitter @az990tony.
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1 localhost commented Trackback

Hey, Tony...instead of all the hand-waving and FUD cast about as if it were fact, just do the math.<div>&nbsp;</div> Writing 8KB blocks 24x7xforever at the maximum write rate the drive can accept and 100% writes (no reads), exactly how long will it take to wear out all the spare cells in a 256GB ZeusIOPS drive formatted to present 200GB of usable capacity (the one EMC is selling), vs. a 256GB flash drive formatted to present only 146GB of usable capacity (as IBM and HDS are trying to sell).<div>&nbsp;</div> Hint - the ZeusIOPS can accept the same number of 8KB writes per second no matter how much usable capacity is presented, and the actual MB/s will stabilize to an identically constant rate on both drives within the first 48 hours.<div>&nbsp;</div> Oh, and remember. The ZeusIOPS drive load balances evenly across ALL 256GB of NAND cells, not just the spares.<div>&nbsp;</div> I say they both last at least 5 years. <div>&nbsp;</div> And that's even with DMX4, V-Max and CLARiiON running the drives at 4Gb/s, while the DS8000 can only support them at 2Gb/s (since the back-end DAs are only 2Gb/s Fibre Channel).<div>&nbsp;</div> Which means IBM is overcharging customers for Flash capacity they can't use. <div>&nbsp;</div> (BTW - I think EMC's street price for the 200GB EFD is lower than IBM's for the 146GB...imagine that!)<div>&nbsp;</div> But go ahead Tony: stop misleading your readers with bogus FUD...<div>&nbsp;</div> DO THE MATH!

2 localhost commented Trackback

By the way, you should really take the time to learn about how wear levelling works on the ZeusIOPS drive before you blog about it.<div>&nbsp;</div> You're demonstrating my point - IBM doesn't get Flash yet. <div>&nbsp;</div> Or at least, YOU don't.<div>&nbsp;</div> There is no situation EVER with the ZeusIOPS drive that you would lose "22GB of cells per year", since the wear-levelling algorithms work to ensure that EVERY CELL WEARS EVENLY. It is virtually IMPOSSIBLE to wear out just one cell (or block) - even if you write to the same LBA millions of times, the drive will actually distribute those writes evenly across ALL of the blocks in the drive.<div>&nbsp;</div> In a mythically perfect world where every NAND cell could accept EXACLTY the same number of program/erase cycles, the ZeusIOPS algorithms have the effect that ALL the cells would fail within a short window of time relateive to each other. <div>&nbsp;</div> And there would be no "re-issue legally as a refurbished 146GB" because the remaining life of the drive would be well below 5 years. Thus it wouldn't be appropriate to resell as a smaller drive (I'm not a lawyer, so I don't know about "legally").<div>&nbsp;</div> If you understood Flash, you'd have known that.<div>&nbsp;</div> But of course, NAND cells don't all have the same exact P/E cycle tolerance. And they have been observed to tolerate well in excess of the rated 100,000 cycles - up to 300,000 to even 2Million in some cases.<div>&nbsp;</div> So the bottom line is that to use these drives effectively, the array actually has to monitor the wear out of cells and adapt/adjust/react appropriately. You haven't mentioned it, so I doubt the DS8000 does this (both DMX and V-Max do).<div>&nbsp;</div> Which means that DS8K customers will indeed be putting there data at higher risk, once IBM actually starts shipping the drives.<div>&nbsp;</div> And of course, no application will write 100% of the time. In fact, with RAID 5, you are GUARANTEED to have to do reads to the drive. But using a mythical 100% 8K write model is appropriate for calculating the MINIMUM lifetime of the drives.<div>&nbsp;</div> Oh, and before you argue that the DS8K will write smaller than 8K (I know it does), doing so in fact wears out the drive faster due to the write-amplification factor (the smallest unit of program/erase on the ZeusIOPS is 4K, and it increases to 8K or 16K depending upon the drive capacity and the formatting). Notably, Symmetrix will always buffer writes and do 8K I/Os, minimizing the effect of write amplification.<div>&nbsp;</div> But of course, since Symmetrix can use up to 80% of global memory as write cache (256GB usable on DMX4, 512GB on V-Max), it will actually do fewer writes to EFDs (and HDDs, for that matter) than the DS8K, given the aging and outdated DS8K's paltry 4GB or 8GB of Non-volitile write cache. Deferring writes and doing writes aligned to the internal structure of the drive minimizes the P/E cycles that the cells experience, further lengthening the life of the drive.<div>&nbsp;</div> Lacking these abilities, DS8K customers are exposed to premature wear-out (and DU/DL) risks that Symmetrix customers need not be concerned with.<div>&nbsp;</div> Those are just some of the advantages customers get by choosing a vendor that actually "gets it", instead of one that merely blogs that they do.<div>&nbsp;</div> So we all are waiting for you to DO THE MATH. <div>&nbsp;</div> And please, be sure to check it twice - maybe even verify it with STEC before you post it. Otherwise you may embarrass yourself and IBM (again).

3 localhost commented Trackback

BarryB,I have distinguished engineers here at IBM to do the math for me. I am sorry that IBM has put you and your colleagues in the uncomfortable position of having to explain or defend EMC's decision on the aggressive 200GB format versus IBM's more conservative 146GB format. <div>&nbsp;</div> -- Tony

4 localhost commented Trackback

Well, then, let's see the math of your Distinguished Engineers!

 
Meanwhile, I'll save the public the agony of anticipation - I've posted <a href="http://thestorageanarchist.typepad.com/weblog/2009/05/2002-meh-ibm-really-really-doesnt-get-flash.html">the quiz answers</a> over on my blog.

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