On Sep 24, 2013, at 7:34 PM, William Brown <william(a)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.