From: "Martin K. Petersen" <martin.petersen@oracle.com>
To: heinzm@redhat.com
Cc: dm-devel@redhat.com
Subject: Re: [PATCH] dm-raid.txt: document discard support
Date: Sat, 08 Aug 2015 12:27:14 -0400 [thread overview]
Message-ID: <yq14mk9iw4d.fsf@sermon.lab.mkp.net> (raw)
In-Reply-To: <1438872279-30693-1-git-send-email-heinzm@redhat.com> (heinzm@redhat.com's message of "Thu, 6 Aug 2015 16:44:39 +0200")
>>>>> "Heinz" == heinzm <heinzm@redhat.com> writes:
Heinz,
> +Discard Support
> +---------------
> +The implementation of discard support amoung hardware vendors varies. When
> +a block is discarded, some storage devices will return zeros when it is
> +read. These devices set the 'discard_zeros_data' attribute. Other devices
> +will return random data. Confusingly, some devices will set
> +'discard_zeros_data', but will still not always return zeros when
> +discarded blocks are read!
This used to be correct but that's no longer the case. We only set
discard_zeroes_data when we have hard guarantees. We no longer
exclusively rely on what the device reports.
discard_zeroes_data is only set if the device reports LBPME/LBPRZ and
uses WRITE SAME 10 or 16 (SCSI) or if it reports DRAT/RZAT and is
explicitly whitelisted (ATA).
--
Martin K. Petersen Oracle Linux Engineering
next prev parent reply other threads:[~2015-08-08 16:27 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-06 14:44 [PATCH] dm-raid.txt: document discard support heinzm
2015-08-08 16:27 ` Martin K. Petersen [this message]
2015-08-12 13:25 ` Heinz Mauelshagen
2015-08-13 17:31 ` Martin K. Petersen
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=yq14mk9iw4d.fsf@sermon.lab.mkp.net \
--to=martin.petersen@oracle.com \
--cc=dm-devel@redhat.com \
--cc=heinzm@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.