Re: [gentoo-user] SSDs, ext4, fstrim, discard ...

[Alan McKinnon <alan.mckinnon@gmail.com>]

On Tue, 11 Oct 2011 22:56:31 +0200
"Stefan G. Weichinger" <lists@xunil.at> wrote:

> 
> As mentioned in the systemd-posting I migrated back to an SSD today
> (on my main rig, the thinkpad uses an SSD happily for a long time
> now).
> 
> A feature in a local magazine updated my knowledge of how to make use
> of the TRIM-command.
> 
> It told me not to use the mount-option "discard" anymore, but run
> fstrim on the mountpoint frequently.
> 
> OK, I learn ;-)
> 
> But, AFAI understand, after trimming sectors/bytes on the
> filesystem/partition, they should be trimmed. I expect X bytes to be
> trimmed at first and if I repeat the command, I expect 0 (or something
> pretty low) bytes to be trimmed then, ok?
> 
> This is what I wonder about:
> 
> ~ # fstrim -v /
> /: 6195433472 bytes were trimmed
> ~ # fstrim -v /
> /: 6195433472 bytes were trimmed
> ~ # fstrim -v /
> /: 6195433472 bytes were trimmed
> 
> 
> I tested it with "discard" on and off.
> 
> / is ext4, yes, and on an SSD, yup.
> 
> Do I misunderstand things here?

Yes, you misunderstand how fstrim works. It's not up to you to say what
it does exactly, it's up to the drive firmware and possibly the kernel.
It's actually fully described in the man page right there in the part
for option -v  :-)

A convenient on-line copy of the man page:

http://www.vdmeulen.net/cgi-bin/man/man2html?fstrim+8


-- 
Alan McKinnnon
alan.mckinnon@gmail.com