RE: SSD Analyzer Tool

Well, I do remember bubble memory...and even core...

I think the concerns are valid, but I also think that IBM has addressed them
in design and automatic allocation and assignment of alternative cells
should a cell fail. As I understand it, this all happens transparent to the
user and there's been considerable testing and contingency planning if and
should these internal failures occur such that there's ample internal
failure space (for lack of a better term) to handle a helluva lot of memory
space fatigue...

I've not heard of any issues with SSD hitting MTBF and failing/faulting to
any unacceptable rate of yet. I spoke with IBM'ers at CES last January on
this and will refresh it next month while in Vegas again. I think what
you'll see in time is substantial SSD for laptop/tablet products and even to
the point of allowing mirroring on laptops in the near future...which is
something for higher end uber-power users that's becoming a must.

DR2

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of DrFranken
Sent: Thursday, December 01, 2011 5:38 PM
To: Midrange Systems Technical Discussion
Subject: Re: SSD Analyzer Tool

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.