From: Ric Wheeler <rwheeler@redhat.com>
To: Mark Lord <liml@rtr.ca>
Cc: Ingo Molnar <mingo@elte.hu>,
Christoph Hellwig <hch@infradead.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Paul Mackerras <paulus@samba.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
xfs@oss.sgi.com, linux-fsdevel@vger.kernel.org,
linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
jens.axboe@oracle.com,
IDE/ATA development list <linux-ide@vger.kernel.org>,
Neil Brown <neilb@suse.de>
Subject: Re: [PATCH, RFC] xfs: batched discard support
Date: Thu, 20 Aug 2009 10:42:09 -0400 [thread overview]
Message-ID: <4A8D60C1.6000809@redhat.com> (raw)
In-Reply-To: <4A8D5FDB.7080505@rtr.ca>
On 08/20/2009 10:38 AM, Mark Lord wrote:
> Ric Wheeler wrote:
>>
>> Note that returning consistent data is critical for devices that are
>> used in a RAID group since you will need each RAID block that is used
>> to compute the parity to continue to return the same data until you
>> overwrite it with new data :-)
>>
>> If we have a device that does not support this (or is misconfigured
>> not to do this), we should not use those devices in an MD group & do
>> discard against it...
> ..
>
> Well, that's a bit drastic. But the RAID software should at least
> not issue TRIM commands in ignorance of such.
If the storage can return different data in a sequence of READ requests of the
same sector (with no writes), there is nothing RAID could do. It would see total
garbage...
> Would it still be okay to do the TRIMs when the entire parity stripe
> (across all members) is being discarded? (As opposed to just partial
> data there being dropped)
This should be safe if the MD bitmaps would prevent us from trying to
READ/regenerate parity for that stripe...
ric
next prev parent reply other threads:[~2009-08-20 14:42 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-08-16 0:47 [PATCH, RFC] xfs: batched discard support Christoph Hellwig
2009-08-16 1:35 ` Mark Lord
2009-08-16 2:19 ` Mark Lord
2009-08-16 2:25 ` Christoph Hellwig
2009-08-16 2:49 ` Mark Lord
2009-08-16 3:25 ` Mark Lord
2009-08-16 13:00 ` Mark Lord
2009-08-16 13:53 ` Christoph Hellwig
2009-08-16 13:59 ` Mark Lord
2009-08-16 14:06 ` Mark Lord
2009-08-16 14:23 ` Christoph Hellwig
2009-08-16 14:26 ` Mark Lord
2009-08-19 20:39 ` Ingo Molnar
2009-08-20 1:05 ` Christoph Hellwig
2009-08-20 1:10 ` Jamie Lokier
2009-08-20 1:38 ` Douglas Gilbert
2009-08-20 1:38 ` Mark Lord
2009-08-21 12:46 ` Ingo Molnar
2009-08-20 1:39 ` Mark Lord
2009-08-20 13:48 ` Ric Wheeler
2009-08-20 14:38 ` Mark Lord
2009-08-20 14:42 ` Ric Wheeler [this message]
2009-08-20 17:19 ` Greg Freemyer
2009-08-20 14:42 ` James Bottomley
2009-08-20 15:43 ` Rolf Eike Beer
2009-08-20 17:00 ` Ric Wheeler
2009-08-20 14:58 ` Douglas Gilbert
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