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From: Bryan Henderson <hbryan@us.ibm.com>
To: Ric Wheeler <ric@emc.com>
Cc: Al Boldi <a1426z@gawab.com>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
	David Chinner <dgc@sgi.com>,
	linux-kernel@vger.kernel.org, Pavel Machek <pavel@ucw.cz>,
	Daniel Phillips <phillips@google.com>,
	Rik van Riel <riel@redhat.com>, Theodore Tso <tytso@mit.edu>,
	Valerie Henson <val.henson@gmail.com>
Subject: Re: [Patch] document ext3 requirements (was Re: [RFD] Incremental fsck)
Date: Thu, 17 Jan 2008 16:31:48 -0800	[thread overview]
Message-ID: <OF3F61F02C.985CCACC-ON882573D4.0001DCF2-882573D4.0002E9F5@us.ibm.com> (raw)
In-Reply-To: <478FE22D.9030907@emc.com>

Ric Wheeler <ric@emc.com> wrote on 01/17/2008 03:18:05 PM:

> Theodore Tso wrote:
> > On Wed, Jan 16, 2008 at 09:02:50PM -0500, Daniel Phillips wrote:
> >> Have you observed that in the wild?  A former engineer of a disk 
drive
> >> company suggests to me that the capacitors on the board provide 
enough
> >> power to complete the last sector, even to park the head.
> >>
> 
> Even if true (which I doubt), this is not implemented.
> 
> A modern drive can have 16-32 MB of write cache. Worst case, those 
> sectors are not sequential which implies lots of head movement.

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


  reply	other threads:[~2008-01-18  0:32 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-08 21:22 [RFD] Incremental fsck Al Boldi
2008-01-08 21:31 ` Alan
2008-01-09  9:16   ` Andreas Dilger
2008-01-12 23:55     ` Daniel Phillips
2008-01-08 21:41 ` Rik van Riel
2008-01-09  4:40   ` Al Boldi
2008-01-09  7:45     ` Valerie Henson
2008-01-09 11:52       ` Al Boldi
2008-01-09 14:44         ` Rik van Riel
2008-01-10 13:26           ` Al Boldi
2008-01-12 14:51         ` Theodore Tso
2008-01-13 11:05           ` Al Boldi
2008-01-13 17:19           ` Pavel Machek
2008-01-13 17:41             ` Alan Cox
2008-01-15 20:16               ` [Patch] document ext3 requirements (was Re: [RFD] Incremental fsck) Pavel Machek
2008-01-15 21:43                 ` David Chinner
2008-01-15 23:07                   ` Pavel Machek
2008-01-15 23:44                     ` Daniel Phillips
2008-01-16  0:15                       ` Alan Cox
2008-01-16  1:24                         ` Daniel Phillips
2008-01-16  1:36                           ` Chris Mason
2008-01-17 20:54                             ` Pavel Machek
2008-01-16 19:06                           ` Bryan Henderson
2008-01-16 20:05                             ` Alan Cox
2008-01-17  2:02                             ` Daniel Phillips
2008-01-17 21:37                               ` Bryan Henderson
2008-01-17 22:45                               ` Theodore Tso
2008-01-17 22:58                                 ` Alan Cox
2008-01-17 23:18                                 ` Ric Wheeler
2008-01-18  0:31                                   ` Bryan Henderson [this message]
2008-01-18 14:23                                     ` Theodore Tso
2008-01-18 15:16                                       ` [Patch] document ext3 requirements (was Re: [RFD] Incrementalfsck) linux-os (Dick Johnson)
2008-01-19 14:53                                         ` Pavel Machek
2008-01-18 15:26                                       ` [Patch] document ext3 requirements (was Re: [RFD] Incremental fsck) Ric Wheeler
2008-01-18 20:34                                         ` Jeff Garzik
2008-01-18 22:35                                           ` Bryan Henderson
2008-01-18 15:08                                     ` H. Peter Anvin
2008-01-18 17:43                                       ` Bryan Henderson
2008-01-16 21:28                         ` Eric Sandeen
2008-01-16 11:51                       ` Pavel Machek
2008-01-16 12:20                         ` Valdis.Kletnieks
2008-01-19 14:51                           ` Pavel Machek
2008-01-16 16:38                   ` Christoph Hellwig
2008-01-16  1:44                 ` Daniel Phillips
2008-01-16  3:05                   ` Rik van Riel
2008-01-17  7:38                     ` Andreas Dilger
2008-01-16 11:49                   ` Pavel Machek
2008-01-16 20:52                     ` Valerie Henson
2008-01-17 12:29                   ` Szabolcs Szakacsits
2008-01-17 22:51                     ` Daniel Phillips
2008-01-15  1:04             ` [RFD] Incremental fsck Ric Wheeler
2008-01-14  0:22           ` Daniel Phillips
2008-01-09  8:04     ` Valdis.Kletnieks

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