linux-kernel - Re: Why is O_DSYNC on linux so slow / what's wrong with my SSD?

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Message-ID: <20131123203600.GA791@amd.pavel.ucw.cz>
Date:	Sat, 23 Nov 2013 21:36:00 +0100
From:	Pavel Machek <pavel@....cz>
To:	Howard Chu <hyc@...as.com>
Cc:	Theodore Ts'o <tytso@....edu>, Chinmay V S <cvs268@...il.com>,
	Stefan Priebe - Profihost AG <s.priebe@...fihost.ag>,
	Christoph Hellwig <hch@...radead.org>,
	linux-fsdevel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
	LKML <linux-kernel@...r.kernel.org>, matthew@....cx
Subject: Re: Why is O_DSYNC on linux so slow / what's wrong with my SSD?

On Wed 2013-11-20 08:02:33, Howard Chu wrote:
> Theodore Ts'o wrote:
> >Historically, Intel has been really good about avoiding this, but
> >since they've moved to using 3rd party flash controllers, I now advise
> >everyone who plans to use any flash storage, regardless of the
> >manufacturer, to do their own explicit power fail testing (hitting the
> >reset button is not good enough, you need to kick the power plug out
> >of the wall, or better yet, use a network controlled power switch you
> >so you can repeat the power fail test dozens or hundreds of times for
> >your qualification run) before being using flash storage in a mission
> >critical situation where you care about data integrity after a power
> >fail event.
> 
> Speaking of which, what would you use to automate this sort of test?
> I'm thinking an SSD connected by eSATA, with an external power
> supply, and the host running inside a VM. Drop power to the drive at
> the same time as doing a kill -9 on the VM, then you can resume the
> VM pretty quickly instead of waiting for a full reboot sequence.

I was just pulling power on sata drive.

It uncovered "interesting" stuff. I plugged power back, and kernel
re-estabilished communication with that drive, but any settings with
hdparm were forgotten. I'd say there's some room for improvement
there...

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