>On Thu, 28 Jul 2005, Andrew Morton wrote: >> Martin Jambor <[EMAIL PROTECTED]> wrote: >> > >> > Do filesystems try to relocate the data from bad blocks of the >> > device? > >Only Windows NTFS, not others AFAIK (most filesytems can mark them during >mkfs, that's all). > >> Nope. Disks will do that internally. If a disk gets a write I/O error >> it's generally dead. > >That's what I thought also for over a decade (that they are basically dead >soon) so originally I disabled NTFS resizing support for such disks (the >tool is quite widely used since it's the only free, open source NTFS >resizer). > >However over the last three years users convinced me that it's quite ok >having a few bad sectors
There's a common misunderstanding in this area. First of all, Andrew and Szakacsits are talking about different things: Szakacsits is saying that you don't have to throw away your whole disk because of one media error (a spot on the disk that won't hold data). Andrew is saying that if you get an error when writing, the disk is dead, and the reasoning goes that if it were just a media error, the write wouldn't have failed -- the disk would have relocated the sector somewhere else and succeeded. Szakacsits is right. Andrew is too, but for a different reason. A normal disk doesn't give you a write error when a media error prevents writing the data. The disk doesn't know that the data it wrote did not get actually stored. It's not going to wait for the disk to come around again and try to read it back to verify. And even if it did, a lot of media errors cause the data to disappear after a short while, so that wouldn't help much. So if a write fails, it isn't because of a media error; i.e. can't be fixed by relocation. The write fails because the whole drive is broken. The disk won't turn, a wire is broken, etc. (The drive relocates a bad sector when you write to it after a previously failed read. I.e. after data has already been lost). As Andrew pointed out, write errors are becoming much more common these days because of network storage. The write fails because the disk isn't plugged in, the network switch isn't properly configured, the storage server isn't up and running yet, and a bunch of other fairly common problems. What makes this really interesting in relation to the question about what to do with these failed writes is not just that they're so common, but that they're all easily repairable. If you had a few megabytes stuck in your cache because the storage server isn't up yet, it would be nice if the system could just write them out a few seconds later when the problem is resolved. Or if they're stuck because the drive isn't properly plugged in, it would be nice if you could tell an operator to either plug it in or explicitly delete the file. But the memory management issue is a major stumbling block. - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
