[kwlug-disc] SSDs and TRIM

John Van Ostrand john at netdirect.ca
Thu Apr 29 12:49:06 EDT 2010

----- "Chris Irwin" <chris at chrisirwin.ca> wrote:

> I just ordered my birthday present: A Solid-State Disk. I made sure I
> got one with TRIM support to try and prevent the performance
> degredation seen with earlier SSDs. Now, TRIM isn't part of ext4
> until
> Linux 2.6.34, so I can't actually have live TRIM support at the
> filesystem layer, but it appears there is a manual utility that can
> be
> used with offline ext2/3/4 filesystems, and apparently online ext4 as
> well. (This is apparently part of hdparm now).
> BUT, has anybody been using TRIM on their LVM-backed filesystems?
> I've
> seen "No, can't be done", "Maybe it should work", and "yes, per the
> instructions in the forum". Of course the dozens of related forum
> threads have dozens of pages to sift through. I've put in a few hours
> of reading, but still have no idea what is going on. From what I
> understand, ext4's TRIM support won't work with LVM since the DM
> layer
> doesn't currently do the mapping. In theory, the third party TRIM
> utilities floating around could do it since they build their own maps
> and sector lists. Anybdoy else looked into this?
> The problem with LVM being that the filesystem isn't a flat map to a
> physical partition, and apparently nobody has done the work to build
> a
> map to redirect TRIM commands.

Correct me if I'm ignorant, but won't putting an LVM on a dm device do what you want? You can use dm for TRIM and have the benefits of LVM.

John Van Ostrand 
CTO, co-CEO 
Net Direct Inc. 
564 Weber St. N. Unit 12, Waterloo, ON N2L 5C6 
Ph: 866-883-1172 x5102 
Fx: 519-883-8533 

Linux Solutions / IBM Hardware 

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