Re: Linux 2.6.3-rc3 - IDE DMA errors on Thinkpad A30

Eric D. Mudama
2004-02-16T19:30:44Z

On Sun, Feb 15 at 22:47, Jeff Garzik wrote:
>Chip Salzenberg wrote:
>>Still: I wonder if the occasional bad sector is really that bad.
>>Shirley, at the unreal densities of today's drives, the development of
>>bad sectors is inevitable? (Especially in a laptop drive that's
>>bounced around in normal use.)
>
>Open argument :)
>
>A lot of smart people will argue that a bad sector every now and again
>occurs, and "I've run my server's disks that way for years."
>
>Other equally smart people argue that modern IDE disks reserve space for
>remapping bad sectors. If you run out of sectors that the drive is
>willing to silently remap for you, you should toss the disk and buy a
>new one.

Yes, definitely. There are a *lot* of spare sectors on a modern IDE
drive -- Running out of spares is an extremely rare event, and usually
indicates that the drive has been operating in severe conditions for
its lifetime. (>55C + vibe sorts of things)

>There is of course the caveat that it is impossible to avoid the drive
>returning "bad sector", instead of silently remapping, on reads.

Yes, because at that point, there's nothing to remap. If the drive
couldn't read it, and knows it isn't in its 2/8MB cache, remapping is
pointless until there is known-good data to apply. Therefore, only on
the write is there a good reason to examine and possibly remap an LBA.

>Oh, and I just thought of something else. Current Linux filesystems
>will, on a read error, usually mark it as a bad sector and move on.
>Really, they should attempt to write to the bad sector before
>considering it bad.
>
>As a result, current kernels will AFAICT assume a sector is bad even
>when the drive politely swaps a good sector in place for you.
>
>One for the todo list, I suppose... a useable workaround for this is
>probably good ole 'e2fsck -c', i.e. badblocks... That says "check again
>to see if this sector is bad", and -hopefully- will unmark bad blocks
>that were incorrectly marked bad.

Agreed.

In most cases, a simpe write to the supposedly-defective LBA will get
the drive to resolve whether it is a permanent media defect that needs
to be remapped, or else functional media that has gone bad for some
other reason. (of which there are several... excessive cold/heat,
vibration, poor power, etc)

--
Eric D. Mudama
edmudama@mail.bounceswoosh.org