Test/verify/repair external disks.

Discussion in 'Mac Accessories' started by ggulliver, Aug 4, 2013.

  1. ggulliver macrumors member

    Jan 22, 2008
    After a power-cut this week, I'm having continuing problems with some partitions of some usb external disks (WD MyBook) on two Macs.

    DiskUtility and DiskWarrior have been useful in fixing some things, but I've still unresolved issues:
    DU is unable to unmount for repair;
    DW reports 'disk in use' and thus isn't able to build a new directory, or 'unable to replace directory' having built a new one.

    These issues are intermittent, and have recurred after fixes with DU and DW, and erasing the partition (but not the entire disk) with DU.

    I'm currently trying to find a way to fsck through terminal, but currently can't get beyond 'it's corrupted, needs repair'.

    The issues have become noticeable during Carbon Copy Cloner backups - where they either fail or complete with error advisories.

    I want to get to the situation of having disks that work reliably, and whilst I think that the issue is 'simply corrupt data that can be fixed by erasing', I'm concerned that the power-cut (and perhaps a preceding spike) have damaged the disks and thus they're likely to prematurely fail.

    I'm reluctant to reformat the entire disks because
    a) I don't have others onto which to load the contents;
    b) Even if I did, with up to 5gb, it'll take days to write.
    c) It'll not show if there's an underlying problem with the disk rather than simply the directory/etcetera.

    Suggestions appreciated. Please and thanks, etcetera.
  2. Fishrrman macrumors G5


    Feb 20, 2009
    Have you tried this:
    1. Power everything down - completely off (disconnect from power source)
    2. Disconnect problem drive(s) from Mac
    3. Power up Mac
    4. Connect ONE of the problem drives to the Mac and power it up. If there is a second drive, leave it disconnected for now.

    What happens next?
    Can you run DiskWarrior on it now?

    In my experience, USB drives seem to be very "fragile" insofar as directory and driver corruption is concerned. It doesn't take much to "mess them up". I will _guess_ that this is due to some kind of "weakness" in USB driver techonology. I can remember in "the old days of Mac" (back in OS 7, 8, 9) the option of "writing a new driver" to a drive. That seems to have disappeared with OS X.

    Sometimes there simply is no other option but to copy whatever data you can to another drive, and then re-initialize, test, repartition, and test again.
  3. ColdCase macrumors 68030

    Feb 10, 2008
    USB protocol is not disk native, adding a bit of overhead which provides more chances for data to get corrupted, especially when power is lost while there is still data in the USB chip stack. USB just adds more opportunity for things to break. But for most, the convenience out weights the performance issues.
  4. ggulliver thread starter macrumors member

    Jan 22, 2008
    Thanks. As DW sometimes runs ok on them, I'd not considered isolating.

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