Re: discard synchronous on most SSDs?

Marc MERLIN
2014-03-16T17:50:16Z

On Sun, Mar 16, 2014 at 12:22:05PM -0400, Martin K. Petersen wrote:
> queued trim, not even a prototype. I went out and bought a 840 EVO this
> morning because the general lazyweb opinion seemed to indicate that this
> drive supports queued trim. Well, it doesn't. At least not in the 120GB
> version:
>
> # smartctl -l gplog,0x13 /dev/sda
> smartctl 5.43 2012-06-30 r3573 [x86_64-linux-3.14.0-rc6+] (local build)
> Copyright (C) 2002-12 by Bruce Allen, http://smartmontools.sourceforge.net
>
> General Purpose Log 0x13 does not exist (override with '-T permissive' option)
>
> If there's a drive with a working queued trim implementation out there,
> I'd like to know about it...

I tried that for you on my 840 EVO 1TB and go the same as you:
legolas:/usr/src# smartctl -l gplog,0x13 /dev/sda
smartctl 6.2 2013-07-26 r3841 [x86_64-linux-3.14.0-rc5-amd64-i915-preempt-20140216c] (local build)
Copyright (C) 2002-13, Bruce Allen, Christian Franke, www.smartmontools.org

General Purpose Log 0x13 does not exist (override with '-T permissive' option)

Now, back to the fact that it takes 1.5sec to delete a kernel tree with
discard on, and it doesn't seem faster with discard off on either that
drive or my very old intel SSD, I'm starting to think that this is kind
of a non problem and/or that something else makes rm of a kernel tree
take around 1.5sec

Is is it much faster on an ssd for someone else?

Marc
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