RE: SSD Analyzer Tool

I have been at IBM Rochester today and I asked Mark Olson what has the results been in the field of the current SSDs, and his reply was the failure rate is about the same as regular disks.

That comes right from the source.

Pete

Pete Massiello
iTech Solutions
http://www.itechsol.com


-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Joe Pluta
Sent: Thursday, December 01, 2011 5:58 PM
To: Midrange Systems Technical Discussion
Subject: Re: SSD Analyzer Tool

I'm not sure what your point is. At no point did I even imply that the system would crash or lose data or anything like that. I assume that when one of these drives goes casters up, you can replace it like any other drive. Even us non-hardware guys replace drives, Larry.

I've only been thinking of the MTBF of the drive vs. the cost and speed. Just wondering about the ROI, is all. No need to get out the long knives. I'd really like to know what the real world MTBF is for an SSD drive vs. other IBM drives, and then do a cost analysis.

I'm not even remotely suggesting IBM would want to put out defective drives. On the other hand, I might think that IBM would LIKE to create a market for a really fast drive that was a little more expensive and needed to be replaced a little more often than the standard drive.

Joe

Does anyone remember bubble memory on AS/400, iSeries, System i or
POWER systems?? I don't.

I know you are not a hardware guy, but really Joe. I ask again, do
you really believe iBM would introduce these things FIRST on their
very largest (and therefore highest profile) machines if they truly
were not ready for prime time? What do you think the publicity would
be for a customer with $10,000,000 of POWER Systems going "Thunk"
because they piled on a ton of data on storage that wasn't really
ready??? I don't see IBM legal letting that even be an option.

- LArry "DrFranken" Bolhuis


On 12/1/2011 5:22 PM, Joe Pluta wrote:

While I like the math, I'm not sure it's entirely that straightforward.
First, you're assuming that the first failure occurs after 3000 writes.
I'm really not sure that's the case or if rather that's more of a
MTBF sort of number. But leaving that, I don't know that simply
multiple the GB by 3000 is going to work. I believe you can only use
the unused part of the disk to rotate your writes. Thought exercise:
if the disk were 80% full and if those files stayed relatively
static, you'd reduce your write pool accordingly. So now you've
dropped your space by a factor of five. Further, I think you have to
deal with fragmentation; either you have to keep a big index of free
space, or you have to effectively have a hard sector size with all that entails.

Personally, I'd be a little leery of dumping all my data to SSD just
yet. I'd probably want the dust to settle just a little bit. We've
gone through this before (does anyone remember "bubble memory")?

Joe

Take a 177GB drive and assume cells can start failing after 3000
writes, there's no slack space/overcapacity, but the drive has a
good wear leveling algorithm. That would suggest you can write
531,000GB before the first cells start to fail. If you figure a 5
year duty cycle for the drive you can write 290GB per day.

Now, extend that by adding in for the slack space. Most SSDs have
7-11% extra capacity but of course it can be higher. Keeping with
the worst-case picture, 7% bumps the daily writes up to 311GB, which
works out to about 13GB/hour or 216MB/minute for every minute, 24 hours per day, for 5 years.

If the IBM drives use SandForce controllers, extend that even more as the
SF controllers do both compression& data deduplication.

If IBM speced cells that are good for 10K writes v. the 3K minimum,
then the writes-before-a-cell-wears-out more than triples.

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