Re: Linux 2.6.29

Linus Torvalds
2009-03-30T20:16:30Z

On Mon, 30 Mar 2009, Rik van Riel wrote:
>
> Maybe a stupid question, but aren't tracks so small compared to
> the disk head that a physical head crash would take out multiple
> tracks at once? (the last on I experienced here took out a major
> part of the disk)

Probably. My experiences (not _that_ many drives, but more than one) have
certainly been that I've never seen a _single_ read error.

> Another case I have seen years ago was me writing data to a disk
> while it was still cold (I brought it home, plugged it in and
> started using it). Once the drive came up to temperature, it
> could no longer read the tracks it just wrote - maybe the disk
> expanded by more than it is willing to seek around for tracks
> due to thermal correction? Low level formatting the drive
> made it work perfectly and I kept using it until it was just
> too small to be useful :)

I've had one drive that just stopped spinning. On power-on, it would make
these pitiful noises trying to get the platters to move, but not actually
ever work. If I recall correctly, I got the data off it by letting it just
cool down, then powering up (successfully) and transferring all the data
I cared about off the disk. And then replacing the disk.

> > And my point is, IT MAKES SENSE to just do the elevator barrier, _without_
> > the drive command.
>
> No argument there. I have seen NCQ starvation on SATA disks,
> with some requests sitting in the drive for seconds, while
> the drive was busy handling hundreds of requests/second
> elsewhere...

I _thought_ we stopped feeding new requests while the flush was active, so
if you actually do a flush, that should never actually happen. But I
didn't check.

Linus