On Tue, Jun 01, 2004 at 08:53:04PM +0000, Charles M. Hannum wrote: > Fix an extremely obvious bug in the handling of the bad block list: the "max" > block was being set 512x further out than it should be, causing rather severe > escalation of the error. Doh! > XXX WTF is the point of this shit, anyway? In most cases, the way you're > supposed to fix a bad block on an ATA disk is to rewrite it -- which will > either just transparently fix it, or spare it. This code actively prevents > that. The point, originally, was to prevent systems and drives grinding themselves into the ground on a read error - potentially causing more damage to the drive in some cases, and in any case taking a long time to never fix the error. Machines could become unusable, even for the administrator trying to fix the problem. Perhaps it's a little ill-conceived: instead of being a hard list of "inacessible" blocks, perhaps it should be more like a negative cache for readable blocks -- but still allow the blocks to be written and potentially fix/remap? Administrator intervention is usually required when a drive has reached the point where this is being triggered, anyway. FWIW, I've found a number of drives that don't seem to remap bad blocks while write-cache is on. I originally suspected bad drive firmware, but I've now confirmed this behaviour across a range of vendors. I know wonder whether we're resetting the command/drive on errors because of too short timeouts, and it never has a chance to complete the process except where the writes are synchronous? I have a little pattern-test script that uses a random-key cgd to dd encrypted-zero's (ie, "random" patterns") over a disk and cmp the decrypted zero's afterwards, then re-key and repeat endlessly. After a cycle or two with write cache off, every "failing" disk I've done this to bar one has recovered and tested clean, and that one disk was very ill indeed. (I don't trust those disks, but I have a lot of /scratch space as a result) -- Dan.
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