From: NeilBrown <neilb@suse.de>
To: Brassow Jonathan <jbrassow@redhat.com>
Cc: "linux-raid@vger.kernel.org Raid" <linux-raid@vger.kernel.org>
Subject: Re: Status of discard support in MD RAID
Date: Mon, 15 Sep 2014 13:44:55 +1000 [thread overview]
Message-ID: <20140915134455.342e5f80@notabene.brown> (raw)
In-Reply-To: <1ED0286A-56DA-491D-853A-1C1045449201@redhat.com>
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On Thu, 11 Sep 2014 18:38:11 -0500 Brassow Jonathan <jbrassow@redhat.com>
wrote:
> Neil (or anyone else),
>
> I know that trim/discard support was added back in 2012 (commit 9db90880). However, I thought there were still issues regarding what happens when various sync operations occur. I'd like to turn on discard support in dm-raid.c (a oneline patch) if things are in order. I can enable any, all or none depending on your recommendation. (I assume RAID1/10 is easier than the parity RAIDs.)
The worst that a sync operation can do is report mismatches and "un-trim"
some (or all) of some devices.
It certainly should never corrupt data.
My perception is that enabling discard support in the filesystem can be good
for some devices and bad for other devices but should always be "safe" even
when not "optimal". I think the same is true for md/raid.
For raid5/6, we only honour discard if the underlying devices report
discarded regions as all-zeros. That make it safe enough I believe.
So I'd suggest: turn it on!
NeilBrown
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prev parent reply other threads:[~2014-09-15 3:44 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-11 23:38 Status of discard support in MD RAID Brassow Jonathan
2014-09-12 0:46 ` Chris Murphy
2014-09-12 9:03 ` David Brown
2014-09-12 9:26 ` Brad Campbell
2014-09-15 3:50 ` NeilBrown
2014-09-12 9:39 ` Roman Mamedov
2014-09-13 20:19 ` Chris Murphy
2014-09-15 3:56 ` NeilBrown
2014-09-15 3:46 ` NeilBrown
2014-09-15 3:44 ` NeilBrown [this message]
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