Re: [9fans] ata drive capabilities

the google paper shows a 40% afr for the first 6 months after some
smart errors appear. (unfortunately they don't do numbers for
a simple smart status.)

Yes, and I rather mischaracterized the google paper's comments on SMART. A reread (I first read them a few months ago) shows the above. Further, the CMU paper even references the google study on the SMART subject:

``They find that [ ... ] the value of several SMART counters correlate highly with failures.''

So SMART appears a little less dumb. I'd say meets the better than nothing criterion.

from my understanding of how google do things, loosing a drive just
means they need to replace it. so it's cheeper to let drives fail.
on the other hand, we have our main filesystem raided on an aoe
appliance. suppose that one of those raids has two disks showing
a smart status of "will fail". in this case i want to know the elevated
risk and i will allocate a spare drive to replace at least one of the
drives.

i guess this is the long way of saying, it all depends on how painful
loosing your data might be. if it's painful enough, even a poor tool
like smart is better than nothing.

I agree (plus I was just wrong about SMART at first), though I do think your example above is about preventing downtime, not so much data loss (Even without smart entirely, and all the disks come up corrupt, we're all backed up within some acceptable window, right?)


what a pity! it would have been so great to have had
an objective assessment of reliability by manufacturer.

Since the CMU thing found no difference between disk *types*, I wonder if it might be that there's little difference between manufacturers either -- instead the difference is in manufacturing, i.e., `vintage' & the like.

i've found it really quite hard to find useful data to
indicate how reliable a drive might be.


I think Fig. 2, Sec. 4.2 of the CMU paper relates to that; the `infant mortality' of manufactured mechanical parts isn't captured in MTTF -- but IDEMA is apparently going to solve this by replacing the single MTTF number that I don't quite understand with 4 different MTTF numbers, one for each `phase' of a disk's life.

--
Josh



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