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To:     Bart Van Assche <bvanassche@acm.org>
Cc:     "Martin K. Petersen" <martin.petersen@oracle.com>,
        John Garry <john.g.garry@oracle.com>, axboe@kernel.dk,
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        Himanshu Madhani <himanshu.madhani@oracle.com>
Subject: Re: [PATCH 01/21] block: Add atomic write operations to
 request_queue limits
From:   "Martin K. Petersen" <martin.petersen@oracle.com>
Organization: Oracle Corporation
Message-ID: <yq1o7heqmk0.fsf@ca-mkp.ca.oracle.com>
References: <20230929102726.2985188-1-john.g.garry@oracle.com>
        <20230929102726.2985188-2-john.g.garry@oracle.com>
        <7f031c7a-1830-4331-86f9-4d5fbca94b8a@acm.org>
        <yq1bkdfrt8l.fsf@ca-mkp.ca.oracle.com>
        <776ff7e4-879f-4967-ba46-fd170804a9e0@acm.org>
Date:   Wed, 04 Oct 2023 14:26:42 -0400
In-Reply-To: <776ff7e4-879f-4967-ba46-fd170804a9e0@acm.org> (Bart Van Assche's
        message of "Wed, 4 Oct 2023 10:28:10 -0700")
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Bart,

> In my opinion there is a contradiction between the above reply and
> patch 19/21 of this series. Data written with the SCSI WRITE ATOMIC
> command is not guaranteed to survive a power failure.

That is not the intent. The intent is to ensure that for any given
application block (say 16KB), the application block on media will
contain either 100% old data or 100% new data. Always.

If a storage device offers no such guarantee across a power failure,
then it is not suitable for use by applications which do not tolerate
torn writes. That is why the writes-are-atomic-unless-there's-a-problem
variant of the values reports in NVMe are of no interest.

-- 
Martin K. Petersen	Oracle Linux Engineering