[Beowulf] SSDs for HPC?

[Joe Landman]

On 4/8/14, 10:25 AM, Ellis H. Wilson III wrote:
> Even in an enterprise environment, there's some very different write
>> patterns possible.  A "scratch" device might get written randomly, 
>> while a
>> "logging" device will tend to be written sequentially.  Consider 
>> something
>> like a credit card processing system.  This is going to have a lot of 
>> "add
>> at the end" transaction data.  As opposed to, say, a library catalog 
>> where
>> books are checked out essentially at random, and you update the "check
>> out/check in" status, and writes are sprinkled randomly through out the
>> data.
>
> I agree, which is what makes wear-leveling such an interesting (and 
> well-researched) area in the SSD field.  However, my suggestion for 
> Prentice on how to use it in his system (keeping the discussion on 
> point) avoided dealing with the wide variety of issues SSD 
> manufacturers have to cope with.
>

Don't add to your level of pain is good advice.

Our experience with SSDs of many types, from consumer through high end 
enterprise grades ... many of the lower end devices do not provide full 
disk semantics.  So things like, I dunno ... lighting up disk access 
LEDs?  Yeah, a fairly large number of them *don't* do that.

No, I am not kidding.  I wish I was.

Intel, to its credit, does.

 From a general purpose point of view, Intel and Samsung make great 
lower end devices.  SanDisk makes great higher end devices.  We are 
working on getting some Toshiba's and a few others for enterprise to 
ultra-high-end testing.

With some of the SSDs, we found that a hot plug event was permanently 
terminal to the device.  Neat, huh?  Other SSDs we played with had 40+% 
failure rates.

>> Sadly, much of this will not be particularly well documented, if at all.
>
> Supposedly more APIs are being exposed to control wear-leveling, when 
> GC kicks, in, etc (I believe Samsung is on the forefront here).  But 
> this is just what I have heard.  I don't have examples to share just 
> yet. Very little has been said in this space in the past because these 
> were the most highly guarded of the proprietary algorithms in the SSD 
> arena.  As more and more algorithms gets researched and are made 
> effectively open-source (i.e., yet another sad case of computer 
> science catching up with industry) pressure is off to protect these so 
> much, and on to give the reigns to the user.

:D

>
> Best,
>
> ellis
>

-- 
Joseph Landman, Ph.D
Founder and CEO
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