On Sun 2014-07-06 21:00:02, Theodore Ts'o wrote: > On Sun, Jul 06, 2014 at 11:37:11PM +0200, Pavel Machek wrote: > > > > Well, when I got report about hw problems, badblocks -c was my first > > instinct. On the usb hdd, the most errors were due to 3.16-rc1 kernel > > bug, not real problems. > > The problem is with modern disk drives, this is a *wrong* instinct. > That's my point. In general, trying to mess with the bad blocks list > in the ext2/3/4 file system is just not the right thing to do with > modern disk drives. That's because with modern disk drives, the hard > drives will do bad block remapping. Actually... I believe it was the right instinct. If I wanted to recover the data... remount-r would be the way to go. Then back it up using dd_rescue. ... But that way I'd turn bad sectors into silent data corruption. If I wanted to recover data from that partition, fsck -c (or badblocks, but that's trickier) and then dd_rescue would be the way to go. > Basically, with modern disks, if the HDD has a hard ECC error, it will > return an error --- but if you write to the sector, it will either > rewrite onto that location on the platter, or if that part of the > platter is truly gone, it will remap to the bad block spare pool. So > telling the disk to never use that block again isn't going to be the > right answer. Actually -- tool to do relocations would be nice. It is not exactly easy to do it right by hand. I know the theory. I had 5 read-error incidents this year. #1: Seagate refuses to reallocate sectors. Not sure why, I tried pretty much everything. #2: 3.16-rc1 produces incorrect errors every 4GB, leading to "bad sectors" that disappear with other kernels #3: Some more bad sectors appear on the Seagate #4: Kernel on thinkpad reports errors in daily check. Which is strange because there's nothing in SMART. #5: Some old IDE hdd has bad sectors in unused or unimportant areas. In #5 the theory might match the reality (I did not check, I trashed the disks). > The badblocks approach to dealing with hardware problems made sense > back when we had IDE disks. But that's been over a decade ago. These > days, it's horribly obsolete. Forcing reallocation is hard & tricky. You may want to simply mark it bad and lose a tiny bit of disk space... And even if you want to force reallocation, you want to do fsck -c, first, and restore affected files from backup. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
