[linux-lvm] Trim support on stripped volumes ?

[linux-lvm] Trim support on stripped volumes ?

[Franck Routier (personnel)]

Hi,

I have set-up of server with 4 SSDs (OCZ Vertex 2) stripped using LVM.
Logical volume has been created using the -i 4 option (iostat confirms
that the 4 disks work in parallel when I write a file).

Ext4 fs is used on the volume, mounted with -discard option.

I am using kernel 2.6.38.

My question is : is there a chance that TRIM command makes its way to
the disks through LVM ? I've read contradictory informations on the web
and I'm sure this is the best place to ask.

My second question is : how would I make _sure_ it works ?
I've found a way to do it with hdparm --fibmap and hdparm --read-sector
here http://askubuntu.com/questions/18903/how-to-enable-trim

But I don't think this can work with LVM. Would there be a similar way
to make sure it is working while using LVM ?

Thanks a lot,

Franck

Re: [linux-lvm] Trim support on stripped volumes ?

[Franck Routier (personnel)]

I found this commit
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=7b76ec11fec40203836b488496d2df082d5b2022
that suggests it could work, but I'm not sure at all...

Franck


Le mardi 24 mai 2011 à 11:20 +0200, Franck Routier (personnel) a écrit :
> Hi,
> 
> I have set-up of server with 4 SSDs (OCZ Vertex 2) stripped using LVM.
> Logical volume has been created using the -i 4 option (iostat confirms
> that the 4 disks work in parallel when I write a file).
> 
> Ext4 fs is used on the volume, mounted with -discard option.
> 
> I am using kernel 2.6.38.
> 
> My question is : is there a chance that TRIM command makes its way to
> the disks through LVM ? I've read contradictory informations on the web
> and I'm sure this is the best place to ask.
> 
> My second question is : how would I make _sure_ it works ?
> I've found a way to do it with hdparm --fibmap and hdparm --read-sector
> here http://askubuntu.com/questions/18903/how-to-enable-trim
> 
> But I don't think this can work with LVM. Would there be a similar way
> to make sure it is working while using LVM ?
> 
> Thanks a lot,
> 
> Franck
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Re: [linux-lvm] Trim support on stripped volumes ?

[Mike Snitzer]

On Tue, May 24 2011 at  5:51am -0400,
Franck Routier (personnel) <alci@mecadu.org> wrote:

> I found this commit
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=7b76ec11fec40203836b488496d2df082d5b2022
> that suggests it could work, but I'm not sure at all...

Yes, that is the commit that added discard support to the stripe target,
it works.

> Le mardi 24 mai 2011 � 11:20 +0200, Franck Routier (personnel) a �crit :
> > Hi,
> > 
> > I have set-up of server with 4 SSDs (OCZ Vertex 2) stripped using LVM.
> > Logical volume has been created using the -i 4 option (iostat confirms
> > that the 4 disks work in parallel when I write a file).
> > 
> > Ext4 fs is used on the volume, mounted with -discard option.

When using -o discard, ext4 will log a warning if a discard failed (and
will disable discards).

So ext4 is a great indicator for whether discards are working on your
striped LV volume.

Mike

Re: [linux-lvm] Trim support on stripped volumes ?

[Franck Routier (personnel)]

Le mardi 24 mai 2011 à 09:14 -0400, Mike Snitzer a écrit :

> When using -o discard, ext4 will log a warning if a discard failed (and
> will disable discards).
> 
> So ext4 is a great indicator for whether discards are working on your
> striped LV volume.
> 

Just out of curiosity, how does ext4 tell if discards is working or
not ?

Re: [linux-lvm] Trim support on stripped volumes ?

[Mike Snitzer]

On Wed, May 25 2011 at  4:11am -0400,
Franck Routier (personnel) <alci@mecadu.org> wrote:

> Le mardi 24 mai 2011 � 09:14 -0400, Mike Snitzer a �crit :
> 
> > When using -o discard, ext4 will log a warning if a discard failed (and
> > will disable discards).
> > 
> > So ext4 is a great indicator for whether discards are working on your
> > striped LV volume.
> > 
> 
> Just out of curiosity, how does ext4 tell if discards is working or
> not ?

It checks the return code from ext4_issue_discard() -- which comes from
sb_issue_discard().  See: fs/ext4/mballoc.c:release_blocks_on_commit()