From: Andrei Borzenkov <arvidjaar@gmail.com>
To: "Austin S. Hemmelgarn" <ahferroin7@gmail.com>,
Robert White <rwhite@pobox.com>,
Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: What if TRIM issued a wipe on devices that don't TRIM?
Date: Fri, 7 Dec 2018 07:09:50 +0300 [thread overview]
Message-ID: <90f90edd-c22c-b36e-4394-5a17b2a986ec@gmail.com> (raw)
In-Reply-To: <6c2a6a00-509d-1585-381f-68582c44591f@gmail.com>
06.12.2018 16:04, Austin S. Hemmelgarn пишет:
>
> * On SCSI devices, a discard operation translates to a SCSI UNMAP
> command. As pointed out by Ronnie Sahlberg in his reply, this command
> is purely advisory, may not result in any actual state change on the
> target device, and is not guaranteed to wipe the data. To actually wipe
> things, you have to explicitly write bogus data to the given regions
> (using either regular writes, or a WRITESAME command with the desired
> pattern), and _then_ call UNMAP on them.
WRITE SAME command has UNMAP bit and depending on device and kernel
version kernel may actually issue either UNMAP or WRITE SAME with UNMAP
bit set when doing discard.
next prev parent reply other threads:[~2018-12-07 4:09 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-06 6:11 What if TRIM issued a wipe on devices that don't TRIM? Robert White
2018-12-06 6:26 ` Roman Mamedov
2018-12-06 10:04 ` ronnie sahlberg
2018-12-06 13:04 ` Austin S. Hemmelgarn
2018-12-07 4:09 ` Andrei Borzenkov [this message]
2018-12-07 12:18 ` Austin S. Hemmelgarn
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