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
Scalable Informatics, Inc.
email: [email protected]
web : http://scalableinformatics.com
twtr : @scalableinfo
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