On Sep 24, 2013, at 7:34 PM, William Brown <will...@firstyear.id.au> wrote:
> 
> Additionally, with the concerns re device shrink. Yes, XFS won't let you
> shrink, but with thin provision LVM that isn't so much an issue: You
> just shrink the pv and leave it alone. I would also argue that anyone
> who is smart enough to shrink their devices, is smart enough to lookup a
> little bit about lvm thinp.

I think LVM thinp commands are a lot more esoteric than ext4, btrfs, or xfs 
resize. But really I think the issue is making it easy for users at install 
time, so as long as the installer doesn't hit a brick wall being unable to 
shrink with the default file system, it probably doesn't matter if it's ext4, 
or XFS on thinp, or btrfs. But right now the installer only supports ext4 
resize.

> 
> I think a really good feature that would go alongside this, would be
> discards by default so that lvm thinp can relinquish free blocks also.
> But that's really another topic :)

So as it turns out some devices get really busy and slow down when TRIM is 
used, so not all devices are well suited for discard and therefore it's 
probably not a good idea for it to be set by default. It's also not enabled by 
default for ssds with btrfs either. And with dm-crypt there's a security 
concern in that it exposes massive zero'd holes on the device instead of 
current data being obscured by stale data.


Chris Murphy
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