On Sat, 25 Dec 2010 00:00:45 +0800, Ian Chapman wrote: > On 24/12/10 11:46, Juan R. de Silva wrote: >> >>> I haven't used badblocks, but suspect that the hard disk drive >>> electronics is clever enough to hide damage and relocate bad sectors. >>> The S.M.A.R.T. electronics will still know they are there, though. >> >> OK. This might be the answer to a question I had: why badblocks never >> found them but smartctl did. > > AFAIK smartctl doesn't actually "detect" bad sectors on a disk, it just > reports what it sees in the SMART counters. Very much true. Bad wording from my part. What I wanted to say that the bad sector was reported by smartctl but was not detected by badsectors, when run on the drive. > The particular counter is > Current_Pending_Sector I believe. Each time the disk encounters > a sector it can't read, the firmware increments this counter. > Only when that bad sector is written to, does the disk remap the sector > and usually Current_Pending_Sector decreases by 1. In my case I never was able to achieve this. I wrote to the sector in question directly with dd, I did it running badblocks in destructive (read/write) mode - the values of Current_Pending_Sector and Offline_Uncorrectable remained still. > I have however seen on occasions, > the counter increase but no bad sector appears to be on the disk. I just > put this down to a temporary glitch, ie the disk at some short point in > time could not read that sector but now it's fine, however the increment > remains. Some drives I believe also increment Reallocated_Sector_Ct > every time a remap is done, but certainly many do it 'silently'. This value for my disk is quite high sinc the drive is 4.5 years old. It's not a lot for a 3.5" drive but is much enough for a laptop drive (Dell Latitude d820) I think. Though I'm still disappointed. I expected it to last more. > You can perform a disk test using smartctl (sounds like you have > already) You bet. :-) > The last value is the LBA which can used with hdparm --write-sector to > write to that specific sector triggering a remap and usually > decrementing the counter. Be extremely careful when using this command > though as a slight mistake can trash data. As I've mentioned in one of my posts, this the only thing I did not do yet. I'll probably do it on the bad sector reported in Current_Pending_Sector (the value is 1) since I know it's starting LBA and I know the block size. But I have no idea what to do with those reported in Offline_Uncorrectable - the value here is 4. And it looks like actually Offline_Uncorrectable gives me more of warning. I looked through my log files and found that it was reported the first with the lower value a couple of months ago. Than a month later it increased, while Current_Pending_Sector remained 1. My bad, I've neglected my log files for a while. -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines
