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From: Markus Binsteiner <makkus@gmail.com>
Date: Mon, 12 Dec 2016 13:12:35 +1300
Message-ID: <CADph71yACvRhb6AWixoaR28+VHZeaGmZqawqY3MSBcSeJM=6Qw@mail.gmail.com>
Subject: Re: btrfs-find-root duration?
To: Chris Murphy <lists@colorremedies.com>
Cc: Btrfs BTRFS <linux-btrfs@vger.kernel.org>
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> You might try 'btrfs check' without repairing, using a recent version
> of btrfs-progs and see if it finds anything unusual.

Not quite sure what that output means, but btrfs check returns instantly:

$ sudo btrfs check /dev/mapper/think--big-home
Checking filesystem on /dev/mapper/think--big-home
UUID: 7f1ce0ed-5986-43ae-b0dd-727eee19fd08
checking extents
checking free space cache
checking fs roots
checking csums
checking root refs
found 655360 bytes used err is 0
total csum bytes: 0
total tree bytes: 131072
total fs tree bytes: 32768
total extent tree bytes: 16384
btree space waste bytes: 123528
file data blocks allocated: 524288
 referenced 524288

When I do the same thing on the root-OS partition that is on the same
disk, it takes a bit longer to complete, and I'm getting:

$ sudo btrfs check /dev/mapper/think--big-jessie
Checking filesystem on /dev/mapper/think--big-jessie
UUID: d82e2746-4164-41fa-b528-5a5838d818c6
checking extents
checking free space cache
checking fs roots
checking csums
checking root refs
found 29295181824 bytes used err is 0
total csum bytes: 27623652
total tree bytes: 973848576
total fs tree bytes: 874446848
total extent tree bytes: 62554112
btree space waste bytes: 154131992
file data blocks allocated: 29202391040
 referenced 30898016256

So I reckon the tree(s) in my home partition is just empty? Why would
btrfs-find-tree take so long to complete though? Also, I've tried to
run btrfs-find-tree on the root-OS partition, but that also didn't
complete within the 10 minutes I tried (so far).

> Although, are there many snapshots? That would cause the rentention of roots.

I can't remember exactly, but it's very possible I didn't use any
snapshots on this machine at all.