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From: Paul Jones <paul@pauljones.id.au>
To: Marc MERLIN <marc@merlins.org>
CC: "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: RE: how to best segment a big block device in resizeable btrfs
 filesystems?
Date: Tue, 3 Jul 2018 00:51:30 +0000
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> -----Original Message-----
> From: linux-btrfs-owner@vger.kernel.org <linux-btrfs-
> owner@vger.kernel.org> On Behalf Of Marc MERLIN
> Sent: Tuesday, 3 July 2018 1:19 AM
> To: Qu Wenruo <quwenruo.btrfs@gmx.com>
> Cc: Su Yue <suy.fnst@cn.fujitsu.com>; linux-btrfs@vger.kernel.org
> Subject: Re: how to best segment a big block device in resizeable btrfs
> filesystems?
> 
> Hi Qu,
> 
> I'll split this part into a new thread:
> 
> > 2) Don't keep unrelated snapshots in one btrfs.
> >    I totally understand that maintain different btrfs would hugely add
> >    maintenance pressure, but as explains, all snapshots share one
> >    fragile extent tree.
> 
> Yes, I understand that this is what I should do given what you explained.
> My main problem is knowing how to segment things so I don't end up with
> filesystems that are full while others are almost empty :)
> 
> Am I supposed to put LVM thin volumes underneath so that I can share the
> same single 10TB raid5?
> 
> If I do this, I would have
> software raid 5 < dmcrypt < bcache < lvm < btrfs That's a lot of layers, and
> that's also starting to make me nervous :)

You could combine bcache and lvm if you are happy to use dm-cache instead (which lvm uses).
I use it myself (but without thin provisioning) and it works well.


> 
> Is there any other way that does not involve me creating smaller block
> devices for multiple btrfs filesystems and hope that they are the right size
> because I won't be able to change it later?
> 
> Thanks,
> 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 ....
>                                       .... what McDonalds is to gourmet cooking
> Home page: http://marc.merlins.org/                       | PGP 7F55D5F27AAF9D08
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