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

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Message-ID: <20200702211653.GB5787@amd>
Date:   Thu, 2 Jul 2020 23:16:54 +0200
From:   Pavel Machek <pavel@....cz>
To:     Ming Lei <tom.leiming@...il.com>
Cc:     Henrique de Moraes Holschuh <hmh@....eng.br>,
        Damien Le Moal <Damien.LeMoal@....com>,
        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-scsi@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH] scsi: sd: stop SSD (non-rotational) disks before reboot

Hi!

> > during a FLASH write or erase can cause from weakened cells, to much
> > larger damage.  It is possible to harden the chip or the design against
> > this, but it is *expensive*.  And even if warded off by hardening and no
> > FLASH damage happens, an erase/program cycle must be done on the whole
> > erase block to clean up the incomplete program cycle.
> 
> It should have been SSD's(including FW) responsibility to avoid data loss when
> the SSD is doing its own BG writing, because power cut can happen any time
> from SSD's viewpoint.

It should be their responsibility. But we know how well that works
(not well), so we try hard (and should try hard) to power SSDs down
cleanly.

In a similar way, it is ext4's responsibility not to corrupt itself,
and we still prefer clean shutdowns.

Plus, HDDs normally do handle unexpected power offs well, but it puts
extra stress on their hardware, so we should avoid that...

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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