Francesco Pretto wrote:
2009/9/18 Andreas Dilger <adilger@xxxxxxx>:
...
Since most disks will internally relocate bad blocks on writes, it is very unlikely that "badblocks" will ever find a problem on a new disk.I'd like to believe you but please read the "smartctl --all" output (attached) for a Toshiba 120GB notebook drive I recently replaced, or just observe this excerpt: 5 Reallocated_Sector_Ct 0x0033 100 100 050 Pre-fail Always - 2 196 Reallocated_Event_Count 0x0032 100 100 000 Old_age Always - 2 .... Num Test_Description Status Remaining LifeTime(hours) LBA_of_first_error # 1 Extended offline Completed: read failure 00% 6366 57398211 # 2 Extended offline Completed: read failure 00% 6350 57398211 So, just 2 sectors reallocated but still read failures that are visible on the linux block device layer.
The disk won't reallocate on a read, only on a write. So this is quite possible.
I can guarantee this: I extensively repeated read tests on the disk, no way I could force the drive to relocate more failing sectors using its own SMART mechanism. So, what I mean is that hw bad blocks relocate features could not work as expected even on modern drives. Because of bugged implementation? Don't know.
No, it's expected. Blocks can only be reallocated on a write (on a read, if it fails, what do you put into the new block? You don't know what was there before so no idea what goes in the new block).
If the unreadable block is not in use on the fileystem, it's ok, because eventually when the fs writes to it the drive should reallocate.
If the unreadable block -is- in use, you're a little stuck; hopefully the fs gives you enough info about which block it is, and you could do a judicious "dd" of /dev/zero into it to force a reallocation, followed by a fsck I guess.
You didn't answer my main question: does ext4 do something in case of a read/write failure that is detected in the block device layer? Exotic filesystems like NTFS (when running Windows, sure) seems to update its bad blocks list online, so it doesn't seems a bad think for notebook/desktop users.
Certainly not in kernelspace (well, it will return an EIO error to you, and possibly abort the filesystem, but that's all).
I've always felt like the badblocks list is a decades-old relic of the floppy days, to be honest.
If you have a sector you can't write to, you're done - the drive would have reallocated if it could, so get what you can off the drive and recycle it.
If you have a sector you can't read, it should be reallocated on the next write.
In neither case is a bad blocks list useful, IMHO. -Eric
The same problem is open for DM users: since evms is deprecated, there's no more a BBR target. So, for example, your buggy hard drive doesn't intercept the first and the only failing sector? The error arrives in the block device layer and the failing drive is deactived/removed from the RAID volume. Not good for me to throw away a disk for just one failing sector. This is matter for another mailing list, so please ignore. Regards, Francesco
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