Default boot/root filesystem

Ric Wheeler rwheeler at
Wed Sep 25 14:56:48 UTC 2013

On 09/25/2013 10:48 AM, Chris Murphy wrote:
> On Sep 25, 2013, at 6:12 AM, Ric Wheeler <rwheeler at> wrote:
>> We should not confuse TRIM that gets handled at the device layer (and is a slow, non-queued S-ATA command for example) and a dm-thin parsing of that same command in software which just updates the metadata that dm-thin maintains.
> Yes, fair point. I should have qualified the assertion better to indicate default discard to the physical device is probably not a good idea. Or maybe it needs to get smarter, and initiated when the fs isn't particularly busy. A kind of delayed discard.
> Chris Murphy

We do have fstrim - you run it periodically on an online file system and it 
sends down larger discard requests.  That is actually pretty much always the 
best way to go.

That said, we definitely could use lots of work on looking at performance on top 
of dm-thin (with/without the discard mount options)....


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