Cc: Al Boldi <a1426z@...>, Alan Cox <alan@...>, David Chinner <dgc@...>, <linux-kernel@...>, Pavel Machek <pavel@...>, Daniel Phillips <phillips@...>, Rik van Riel <riel@...>, Theodore Tso <tytso@...>, Valerie Henson <val.henson@...>
Ric Wheeler <ric@emc.com> wrote on 01/17/2008 03:18:05 PM:
drive
enough
We weren't actually talking about writing out the cache. While that was
part of an earlier thread which ultimately conceded that disk drives most
probably do not use the spinning disk energy to write out the cache, the
claim was then made that the drive at least survives long enough to finish
writing the sector it was writing, thereby maintaining the integrity of
the data at the drive level. People often say that a disk drive
guarantees atomic writes at the sector level even in the face of a power
failure.
But I heard some years ago from a disk drive engineer that that is a myth
just like the rotational energy thing. I added that to the discussion,
but admitted that I haven't actually seen a disk drive write a partial
sector.
Ted brought up the separate issue of the host sending garbage to the disk
device because its own power is failing at the same time, which makes the
integrity at the disk level moot (or even undesirable, as you'd rather
write a bad sector than a good one with the wrong data).
--
Bryan Henderson IBM Almaden Research Center
San Jose CA Filesystems
--
