Re: Why is O_DSYNC on linux so slow / what's wrong with my SSD?
From: Ric Wheeler
Date: Sat Nov 23 2013 - 18:01:44 EST
On 11/23/2013 03:36 PM, Pavel Machek wrote:
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
Hi Pavel,
When you drop power, your drive normally loses temporary settings (like a change
to write cache, etc).
Depending on the class of the device, there are ways to make that permanent
(look at hdparm or sdparm for details).
This is a feature of the drive and its firmware, not something we reset in the
device each time it re-appears.
Ric
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/