linux-kernel - Re: [PATCH] scsi: sd: stop SSD (non-rotational) disks before reboot

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Message-ID: <20200705213125.GC8285@khazad-dum.debian.net>
Date:   Sun, 5 Jul 2020 18:31:25 -0300
From:   Henrique de Moraes Holschuh <hmh@....eng.br>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Simon Arlott <simon@...iron.net>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Jonathan Corbet <corbet@....net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-scsi@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH] scsi: sd: stop SSD (non-rotational) disks before reboot

On Thu, 18 Jun 2020, Christoph Hellwig wrote:
> > For SSDs, I don't think an extra stop should ever be an issue.
> 
> Extra shutdowns will usually cause additional P/E cycles.

I am not so sure.  We're talking about enforcing clean shutdowns here
(from the SSD PoV).

A system reboot takes enough time that the SSD is likely to do about the
same amount of P cycles commiting to FLASH any important data that it
would trigger by a shutdown sequence, simply because it should not keep
important data in RAM for too long.  By extension, it would not increase
E cycles either.

OTOH, unclean shutdowns *always* cause extra P/E, and that's if you're
lucky enough for it to not cause anything much worse.

-- 
  Henrique Holschuh