SuperMicro H8SSL-i (ServerWorks HT1000) -- JMR SATAStor 6x2.5" in 1x5.25" array

[Bryan J. Smith]

On Sat, 2005-12-03 at 17:24 -0500, Mark Hahn wrote:
> can you cite your source for the statement that MTBF is .4 Mhours?

You can assume I'm pulling it out of my ass if you like.  ;->

First off, it's commonly known that "commodity" drives are rated for
50,000 restarts @ 8 hours/start, resulting in the 400,000 hours MTBF.
Although there have been improvements in thermal tolerances (e.g., 40C
to 60C and vibration (typically 2-3x) in commodity drives over the last
few years, the MTBF ratings have _not_ improved.  That's why the 50,000
restarts number _still_ exists in _all_ commodity drives these days,
including the latest Seagate Barracuda 7200.9 line and the Hitachi
Deskstar 7K500 line.

Secondly, the new generation of tolerance-tested "commodity" drives are
rated for 1,000,000 hours MTBF.  Still the same 50,000 restarts, but in
a "network managed 24x7" environment with better cooling and cycling
(the most detrimental aspects of a desktop) than a desktop.  These
include the Seagate NL35 line, which rolls off the same technology lines
as the previous Seagate Barracuda 7200.8.  Now I haven't checked if a
new NL series is available matching the 7200.9, but typically they lag
giving the cutting edge line time to mature and find ways of
guaranteeing effective tolerance testing for identifying candidates for
the NL model.

Lastly, pull up just about _any_ technical specification for _any_
Hitachi, Seagate, etc... "commodity" hard drive.  IBM and, now, Hitachi
actually has some models (namely many Desktar) that state the warranty
is invalid if the drive is operated more than 14 hours/day -- a
post-75GXP policy.  (I'm sure they can't hold consumers to that, but
they can system integrators who sell their Deskstar models in systems
designed for 24x7 operation).

Now that's all 

> I know that was a common figure for desktop drives from 8-10 years ago, 

First off, the 0.4M and 1.4M number is extremely recent -- last 3 years.

Secondly, the 0.4M number for desktop drives was _only_ when the drive's
ambient did _not_ exceed 40C until just recently.  The new crop of
"commodity" mechanics developed and deployed in just the last 12-18
months can now take up to 60C ambient.  That radically improves
reliability.

Third, the 1.4M number is for the "enterprise" drives which have
_always_ been rated for 55+C ambient -- pretty much standard in the last
8+ years -- and have drastically reduced vibration.  I.e., the platters
are not cutting-edge density, but high spindle which often dictates far
more refined assembly (with associated cost).

Lastly, have you ever seen the "real world" number of desktop hard drive
replacements on the _latest_ systems that are allegedly the new 60C
rated material?  Just this past year -- with _new_ systems -- at Boeing
in St. Louis, we saw over a 20% failure rate in just 3 months, over a
30% failure rate in 6 months, with Dell and HP systems used by
engineers.  A colleague of mine with Disney's POS division in Orlando --
just this past year -- has seen almost a 40% failure rate in 6 months.

Now one could say that a retail box might have a lower failure rate than
a tier-1 PC OEM desktop box.  One might also say that engineering and
POS systems are more heavily used.  But even then, those rates of
failure do _not_ bode well for the 400,000 hour MTBF number average!
They are dying well in advance of 50,000 restarts, even when the systems
are never run more than 14 hours/day.

> but I do also remember seeing a number of ATA disks that claimed MTBF's 
> around 1Mhour.  
> I'm guessing you just figured that 
> 	1.4 Mhour * (10*5)/(24*7) = .417 Mhour

No, hit just about _any_ technical specification, 50,000 restarts.  Most
vendors do _not_ list the "raw" MTBF on commodity disks anymore, as they
want to make _no_ guarantees!  If you get into the nitty-gritty of their
warranty policies, there's little they can do with regards to consumers.

But when it comes to system integrators and vertical applications --
where their products can be proven to require more than 50,000 @ 8
hours/day -- they have very, very strict replacement policies.  Which is
where the new Seagate NL series, Western Digital Caviar RE, etc... all
come in.

> but it would be nice to have even a hint of actual, factual MTBF's.

Again, assume I'm pulling them out of my ass.  ;->

Reality:  Outside of the 1.4M for "enterprise" drives, and 1.0M for the
new crop of "Near Line" rated, tolerance-tested commodity drives, you
will _not_ find _any_ guarantee of MTBF.

Only 50,000 restarts.  ;->



-- 
Bryan J. Smith   mailto:b.j.smith at ieee.org
http://thebs413.blogspot.com
------------------------------------------
Some things (or athletes) money can't buy.
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