On Mon, Jul 02, 2018 at 12:59:02PM -0400, Austin S. Hemmelgarn wrote:
> > Am I supposed to put LVM thin volumes underneath so that I can share
> > the same single 10TB raid5?
>
> Actually, because of the online resize ability in BTRFS, you don't
> technically _need_ to use thin provisioning here. It makes the maintenance
> a bit easier, but it also adds a much more complicated layer of indirection
> than just doing regular volumes.
You're right that I can use btrfs resize, but then I still need an LVM
device underneath, correct?
So, if I have 10 backup targets, I need 10 LVM LVs, I give them 10%
each of the full size available (as a guess), and then I'd have to
- btrfs resize down one that's bigger than I need
- LVM shrink the LV
- LVM grow the other LV
- LVM resize up the other btrfs
and I think LVM resize and btrfs resize are not linked so I have to do
them separately and hope to type the right numbers each time, correct?
(or is that easier now?)
I kind of linked the thin provisioning idea because it's hands off,
which is appealing. Any reason against it?
> You could (in theory) merge the LVM and software RAID5 layers, though that
> may make handling of the RAID5 layer a bit complicated if you choose to use
> thin provisioning (for some reason, LVM is unable to do on-line checks and
> rebuilds of RAID arrays that are acting as thin pool data or metadata).
Does LVM do built in raid5 now? Is it as good/trustworthy as mdadm
radi5?
But yeah, if it's incompatible with thin provisioning, it's not that
useful.
> Alternatively, you could increase your array size, remove the software RAID
> layer, and switch to using BTRFS in raid10 mode so that you could eliminate
> one of the layers, though that would probably reduce the effectiveness of
> bcache (you might want to get a bigger cache device if you do this).
Sadly that won't work. I have more data than will fit on raid10
Thanks for your suggestions though.
Still need to read up on whether I should do thin provisioning, or not.
Marc
--
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
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Home page: http://marc.merlins.org/ | PGP 7F55D5F27AAF9D08
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