From: "Martin K. Petersen" <martin.petersen@oracle.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Eric Sandeen <sandeen@sandeen.net>,
Carlos Maiolino <cmaiolino@redhat.com>,
xfs@oss.sgi.com
Subject: Re: [PATCH] libxfs: Get Physical Sector Size instead of Logical Sector size
Date: Mon, 28 Nov 2011 11:08:29 -0500 [thread overview]
Message-ID: <yq1vcq4grgi.fsf@sermon.lab.mkp.net> (raw)
In-Reply-To: <20111127235051.GX2386@dastard> (Dave Chinner's message of "Mon, 28 Nov 2011 10:50:51 +1100")
>>>>> "Dave" == Dave Chinner <david@fromorbit.com> writes:
>> Ok, if we have mismanaged the alignment and aligned to logical, not
>> physical, then I guess there would be an issue... but at that point
>> we've already messed up (though not catastrophically I guess)...
Dave> That's where I'm concerned - if alignment is screwed because the
Dave> FS is 512B sector aligned (because something read the logical
Dave> sector size), then using a 4k sector will result in torn writes
Dave> because every 4k sector write is potentially made up of 2 4k write
Dave> IOs, not 1.
There's another inherent failure scenario with 512b logical / 4096b
physical. If you write in 512-byte multiples and experience a medium
error you can lose the sibling logical blocks within that physical
block. You'll get an I/O error back but there are no means to
communicate that you have also lost blocks that were not part of your
write request. So if you use 512-byte entries in the journal and get a
write error you should at the very minimum consider adjacent entries
inside a 4KB window suspect.
Dave> That's my concern - using the logical 512b sector size is -always-
Dave> safe, but using the 4k physical block size is only safe if
Dave> everything under the filesystem has detected and used the physical
Dave> block size of the disk for alignment and sector sizes...
You should always take alignment into account.
And while Christoph is right that (thankfully) nobody ended up shipping
drives with 1-alignment by default, most 512e drives have the alignment
jumper and some people actually use it.
--
Martin K. Petersen Oracle Linux Engineering
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next prev parent reply other threads:[~2011-11-28 16:09 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-24 19:20 [PATCH] libxfs: Get Physical Sector Size instead of Logical Sector size Carlos Maiolino
2011-11-24 19:50 ` Carlos Maiolino
2011-11-27 1:06 ` Dave Chinner
2011-11-27 23:05 ` Eric Sandeen
2011-11-27 23:50 ` Dave Chinner
2011-11-28 7:56 ` Christoph Hellwig
2011-11-28 16:08 ` Martin K. Petersen [this message]
2011-11-28 16:11 ` Eric Sandeen
2011-11-29 17:15 ` Martin K. Petersen
2011-11-29 17:38 ` Eric Sandeen
2011-11-30 0:19 ` Dave Chinner
2011-11-30 15:03 ` Carlos Maiolino
2011-11-28 16:56 ` Greg Freemyer
2011-11-28 7:54 ` Christoph Hellwig
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