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Message-ID: <alpine.LFD.2.00.0903301259490.4093@localhost.localdomain>
Date: Mon, 30 Mar 2009 13:05:54 -0700 (PDT)
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Rik van Riel <riel@...hat.com>
cc: Ric Wheeler <rwheeler@...hat.com>,
"Andreas T.Auer" <andreas.t.auer_lkml_73537@...us.ath.cx>,
Alan Cox <alan@...rguk.ukuu.org.uk>,
Theodore Tso <tytso@....edu>, Mark Lord <lkml@....ca>,
Stefan Richter <stefanr@...6.in-berlin.de>,
Jeff Garzik <jeff@...zik.org>,
Matthew Garrett <mjg59@...f.ucam.org>,
Andrew Morton <akpm@...ux-foundation.org>,
David Rees <drees76@...il.com>, Jesper Krogh <jesper@...gh.cc>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.29
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
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