[Tfug] NAS suggestions
bexley401 at yahoo.com
Sat Oct 20 03:36:53 MST 2012
--- On Fri, 10/19/12, Angus Scott-Fleming <angussf at geoapps.com> wrote:
> On 14 Oct 2012 at 21:32, Zack Williams wrote:
> > Just an FYI - for large disks, there a not-insignificant change of
> > data corruption when doing RAID rebuilds:
> > http://queue.acm.org/detail.cfm?id=1670144
> This is another interesting article on modern drives and RAID:
> Data Storage: The Myth of Redundancy - Datamation
Yes, I think for RAID to survive, disk interfaces either need to
get a lot *wider* (which has not been the trend!) to dramatically
increase bandwidth to/from the medium *or* drives must internally
implement the redundancy (pray for no spindle failures -- redundant
E.g., return to the days when disks could pull data off 100+
cylinders at the same time! (actually makes sense if you
*know* the drive is destined for a RAID array and can, therefore,
be more predictive of access patterns)
Of course, adding complexity also runs the risk of making things
more brittle -- until that technology matures.
It just takes too long to rebuild a failed RAID array. It assumes
you can *spot* the failure, quickly. And, are comfortable going
through the steps to rebuild it (i.e., lots of experience/practice
And, *how* you store the data also affects recoverability.
E.g., a bit flip in the middle of an ASCII file can *probably*
be recovered (by a sentient being) a lot more reliably than
a bit flip in that same file *gzip-ed*!
Finally, the consequences of particular errors can vary greatly.
E.g., have a mailing address change from "1313 Mockingbird Ln"
to "1312 Mockingbird Ln" will probably never be noticed (i.e.,
your mail will still get delivered by the letter carrier).
Similarly, a "deposit" appearing to have been recorded as
$1025.47 instead of $1.47 will likely be discoverable when
someone/thing notices the balance is off by $1024!
To date, I've had one disk fail completely (i.e., fail to spin up)
and, (just recently) another exhibiting unrecoverable data error(s).
Since these were "working disks" (not archive disks), it was a
simple matter to replace them (I've not yet finished examining
this recent failure to see the extent of the problem).
OTOH, I did have an experience some years (20?) ago with an OS
bug *trashing* disks (superblock corruption?).
Moral of story: don't place much value on data! :>
(Conversely, if you place value on the data, then be prepared
to put a corresponding amount of *money* on the line, as well!)
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