[sclug] My disk esplode

Dickon Hood sclug at splurge.fluff.org
Tue Apr 15 00:41:37 UTC 2008

On Tue, Apr 15, 2008 at 01:11:40 +0100, David Given wrote:
: Dickon Hood wrote:
: [...]
: > : At this point I needed to take an image of the hard disk. dd would not
: > : work, because dd doesn't handle I/O errors appropriately.

: > dd if=... of=... conv=noerror,sync

: > Bad blocks are replaced with zero bytes, and it all works as well as can
: > be expected.  Likely one of the two tools you mention below do little more
: > than this.

: Ah, I didn't know the sync option caused it to replace the bad blocks
: with zeroed blocks --- noerror alone just omits them, with catastrophic
: results on disk images!

Yup -- I've never seen the point of that.

: ddrescue is actually fairly clever; it will as rapidly as possible read
: the working parts of the disk, and then binary chops the non-working
: bits down to individual sectors and will keep retrying them until they
: work (or you tell it to stop). It also keeps ongoing logfiles so it can
: resume where it left off if you tell it to stop. Dead handy.

Ah, it's that.  Yes, I've heard of it.

: [...]
: > It's quite simple, people: one copy of the data is no copy at all.  You
: > have no backup, and you have no guarantee that the data you think you have
: > is available.

: Indeed. But I *am* a home user, not a professional one; the data is not
: of monetary worth, merely inconvenient to replace; and I don't want to
: pay twice as much for my disk space (although that's less of an issue
: these days). This was the first disk I've *ever* had that's died. Also,
: RAID over USB is a pain in the arse.

But how inconvenient has it been?  If you've spent more than a couple of
hours on it, you would probably have been better off buying two.

Over the years, I've had more discs fail on me than I care to remember;
I'm probably a little paranoid about failures these days, but it's saved
me rather a lot.  I, like most people, have little interest in taking
(managing) backups, and as such, I've had a lot of success with data
replication.  It's not a solution to the dataloss problem, but it is far,
far more reliable than having just the one disc.  In your case, you appear
not to have had either.

: If the SMART had worked, the disk would have moaned at me *before* it
: went wrong and given me time for me to do something about it. I suspect
: I may invest in a SATA external card and then buy SATA disks in future.
: Faster, too...

There is that.  I wasn't aware that SMART didn't work over USB, but I
suppose I should have guessed.  USB Mass Storage is little more than the
basic SCSI command set over a USB transport, but it's missing all the nice
bits.  SATA is a better subset of the SCSI command set over a much, much
better transport, but still not as good.

: (Incidentally, please don't cc me when you reply to the list, people; I
: don't need two copies...)

Apologies; I tend to hit 'g' by default and be done with it.

Dickon Hood

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