Disk utility warnings reliable?

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tpprynn
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Disk utility warnings reliable?

Post by tpprynn »

I've bought a second hand laptop, which seemed fine but I get warnings using the disk utility about 'many bad sectors' and relocated sectors. the only other time I've had this, with the same, Toshiba brand of drive, when then using Windows-compatible tools the disk checked out fine. I'm not as automatically mistrustful of Windows software as some people and this is SeaTools, not MS's own thing. From some googling I'm open to the possibility that this arises from Linux filesystem practices, and the first of the drives I mention showed no unhealthy signs till I started on the Linux path. Not what people want to hear, I know, but if it needs fixing...

This is a zif-pata 1.8 drive, as I think are also used in iPods, at least older ones, if this makes any difference. Not super-easy to come by either.

Thanks.

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xenopeek
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Re: Disk utility warnings reliable?

Post by xenopeek »

If the disk utility is finding bad sectors, that means parts of your hard disk are permanently damaged. Any bad sectors are physical damage, not caused by whichever file system you choose to use. From the hard disk being PATA, I'm assuming its old. This is what happens to old hard disks, especially in mobile devices. Hard disks don't live forever :( (It is just that usually they get replaced before you notice any failures. And modern hard disks have a "spare area", which they use to replace any bad sectors without your OS noticing it.) Probably it doesn't have SMART, or only partially implemented, but have a look at if the SMART Data says anything (there is a button for it when you click on your hard disk in the disk utility). SMART Data is reported by the hard disk itself, as it monitors its own health.
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tpprynn
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Re: Disk utility warnings reliable?

Post by tpprynn »

Yes it has Smart data, that's where the bad news came from.

I'm now half way through running CHKDSK in Windows 7, I'll see what it says.

Not sure what to do about it yet, it's an otherwise great laptop - new ones are looking increasingly annoying, cheap and sparkly - and I am curious about an SSD, even a modest one, which still being odd size and adaptor, a minority interest product, it will need to be. This drive is a 4200rpm one as well, by the way. This morning I'd never heard of zif-pata or drives slower than 5400rpm...

Thanks.

srs5694
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Re: Disk utility warnings reliable?

Post by srs5694 »

First, SMART utilities have been known to give false positives. There were problems with that a year or two ago with some Linux utilities. I'm not sure how common this problem is or was, though. Some disks (particularly some Seagate models, IIRC) report values that require unusual interpretation -- they can look as if they've got ridiculously high numbers of bad sectors because Seagate splits the field and uses the high bits for a different purpose than the low bits. If the SMART utility doesn't know this, it can look like the disk is bad when in fact it's fine.

Second, CHKDSK might or might not catch any problems; it (and Linux's fsck) just check filesystem data structures. If a disk has bad sectors, those sectors might or might not cover the filesystem data structures; they might be in files themselves or in parts of the disk that are completely unused at the moment -- but that might be called upon to hold data tomorrow. Thus, to get a real feel for whether the disk is reliable, you should:
  • Run a "long" SMART test, which scans the entire disk's surface. This will probably take at least an hour, and it should help SMART update any data it's got. If something is just starting to go, this test might produce more reliable SMART data that more clearly indicates an impending failure.
  • Run a non-SMART test by attempting to read the whole disk. Something like "dd if=/dev/sda of=/dev/null" should do the trick. If it returns errors because of corrupt data (rather than just reaching the end of the file), then you know you've got a problem that goes beyond a few sectors that the disk might automatically re-allocate. Ideally, you can do a similar write test ("dd if=/dev/zero of=/dev/sda"), but this will be destructive, at least as performed by dd in this way. There are more specialized disk testing tools you can use, some of which can do non-destructive read/write tests by reading a sector and then writing it back.
Keep in mind that SMART was intended to detect disk problems before they become serious enough to cause data loss. Thus, if SMART is reporting problems but a "dd" test doesn't report errors, it could be that the disk is starting to go bad, but it's not yet bad enough to cause data loss. The situation could change in a week, though, which is why my inclination is to replace a disk if SMART says somethng is wrong with it, even if it's not losing files.

tpprynn
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Re: Disk utility warnings reliable?

Post by tpprynn »

That was pretty comprehensive, thanks!

My earlier drive had 18 bad sectors, whereas this time it's a ten or fifteen digit number, which might fit 'ridiculously high'. The disk makes a click every few seconds for a while (not like the quiet sound like an old watch being wound up that some older drives make normally), then stops that for a period. I've seen how all drives have different sounds but this doesn't sound too encouraging.

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