Re: SSD Analyzer Tool

Joe,

I put some SSDs in a Power6 520 2 years ago, it is an I/O intensive machine. We moved all the heavy I/O files to the SSDs, performance is great, and we haven't replaced one SSD yet. I enjoyed reading all your technical specs, just reporting what I have out in the field.

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 12:40 AM
To: Midrange Systems Technical Discussion
Subject: Re: SSD Analyzer Tool

"Reliable enough" leaves a whole lot of room. The problem with reliability is the number of charge states required per cell. SLC devices store one bit per cell and so you either need on or off; it's pretty simple. MLC devices typically store two bits per cell, and so require four identifiable states and those degrade pretty quickly. The numbers I've seen are somewhere around between 3000 and 10,000 writes (as opposed to 100,000 for SLC). That's NOT a lot of writes unless you have a really, really good load leveling algorithm. Not to mention MLC is much slower. I think IBM uses eMLC, which is a compromise design with more writes but is even slower still especially on writes.

So, back to the question at hand, what's "reliable enough"? We update our item master with every shipment. We ship hundreds of times a day.
To have cells die after a few thousands writes is awfully frightening.
On the other hand, for a mostly read-only drive like a load source there's something to be said for SSD. I'm designing my next workstation and I may go with two different SSD drives, one for boot / program load and one for a scratch drive (things like workspaces for my Rational products). The thought is that the scratch drive can be replaced as needed without affecting the load partition, and I'll have a traditional hard drive to store low-priority data and also to back up the SSDs.

Joe

The original 70GB SSDs were SLCs as I recall. These were actually
128GB devices leaving significant capacity for re-maping worn out areas.

The current 177GB SSDs are MLC devices. I don't have information on
the overcapacity of these devices but suspect perhaps 256GB is the likely size.

IBM would not ship an enterprise class device on POWER systems if they
did not believe that they were reliable enough for the task at hand.

- Larry "DrFranken" Bolhuis

On 11/30/2011 10:18 PM, Joe Pluta wrote:

What kind of SSDs are they? SLC or MLC? Any information on how long
they last? Because the MLCs are notoriously short-lived. A lot of
that depends on the data use algorithms.

Joe