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SubjectRE: [PATCH] brd: Refuse improperly aligned discard requests
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> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-
> owner@vger.kernel.org] On Behalf Of Jan Kara
> Sent: Wednesday, November 4, 2015 10:14 AM
> To: axboe@kernel.dk
> Cc: LKML <linux-kernel@vger.kernel.org>; linux-fsdevel@vger.kernel.org;
> Christoph Hellwig <hch@infradead.org>; Jan Kara <jack@suse.com>
> Subject: [PATCH] brd: Refuse improperly aligned discard requests
>
> Currently when improperly aligned discard request is submitted, we just
> silently discard more / less data which results in filesystem corruption
> in some cases. Refuse such misaligned requests.

I agree discarding more than requested is very bad.

If they are routed to SCSI or ATA devices, though, the discard commands
(SCSI UNMAP or ATA DATA SET MANAGEMENT/TRIM) are just hints, so there
is no guarantee the discard will do anything. Are you finding
filesystems that still don't understand that? dm-raid held that
mistaken assumption for a long time.

---
Robert Elliott, HP Server Storage



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