[Beowulf] dedupe filesystem

Mark Hahn hahn at mcmaster.ca
Fri Jun 5 18:07:12 EDT 2009


>> IMO, this is a dubious assertion.  I bought a couple incredibly cheap
>> desktop disks for home use a couple weeks ago: just seagate 7200.12's.
>
> Are you happy with the 7200.12 so far? I must admit the awful 7200.11 (the 1 and
> 1.5 TByte variety) has quite soured me on Seagate. I haven't had any problems
> with WD so far (I'm strictly using RE3 and RE4's, though).

7200.x's are clearly just desktop disks - I wouldn't necessarily build
a large raid out of them, or expect to run them 24x7 for years.  but 
these days, you really have to regard disks as cheap consumables, at least
if you're not pushing max size or enterprise models.  I had myself talked
into wd re's as well, but then I realized that a few 7200.12's are just
to cheap to care - es.# and re# lines cost over twice as much.  and if we're
talking about $50 disks, is it really worth talking about?

I have no reliability experience yet.  it's clear though that disk vendors have 
heard all the discussions on how URE/NRE rates limit the usability of large
raid arrays.  (ie, 7200.12's are "1 NRE per 10e14 bits read".  I wonder
whether they mean just 10^14, since 10e14 should be normalized to 1e15...)
in any case, my home array is not going to be close to either 12.5 or 125 TB, 
so I don't worry about the too-big-to-rebuild-without-URE issue.  but I did
notice that some drive lines (wd caviar black) actually appear to increase 
the ECC on bigger models.  the 500/640G models are rated as <1 in 10^14,
but the 750/1000 step up to <1/10^15.  the sustained bw drops from 113 to 106
MB/s, supporting the idea...

regards, mark hahn.
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