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Subject: Re: BTRFS constantly reports "No space left on device" even with a
 huge unallocated space
To: Chris Murphy <lists@colorremedies.com>
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From: Jeff Mahoney <jeffm@suse.com>
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From: Jeff Mahoney <jeffm@suse.com>
To: Chris Murphy <lists@colorremedies.com>
Cc: Ronan Arraes Jardim Chagas <ronisbr@gmail.com>,
 Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com>,
 Btrfs BTRFS <linux-btrfs@vger.kernel.org>,
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Message-ID: <52290114-3b37-2de5-9c9f-ceda6dff955b@suse.com>
Subject: Re: BTRFS constantly reports "No space left on device" even with a
 huge unallocated space
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On 8/31/16 5:48 PM, Chris Murphy wrote:
> OK it looks like with -w flag I can get a reliable indication of
> whether quota is enabled or not:
>=20
> [root@f24s ~]# btrfs quota enable /mnt/0
> [root@f24s ~]# btrfs quota rescan -w /mnt/0
> quota rescan started
> [root@f24s ~]# btrfs quota disable /mnt/0
> [root@f24s ~]# btrfs quota rescan -w /mnt/0
> ERROR: quota rescan failed: Invalid argument
>=20
>=20
> So if you did not enable quota support, and aren't sure if it's
> enabled you can try 'btrfs quota rescan -w <mp>' but this might
> actually be a bad idea, a rescan could take a while if you're actually
> using quotas, I have no idea because I don't use them.

It can take a while, but the code is smart enough not to get too much in
the way of other activity.  It maintains a progress marker and only does
live accounting on extents that have already been scanned.

> Perhaps someone can point out an easier way to determine whether
> quotas are enabled?

btrfs qgroup show <path>

If you get a message like:
ERROR: can't perform the search - No such file or directory
ERROR: can't list qgroups: No such file or directory

=2E.. it means there's no quota root and thus quotas aren't enabled.

-Jeff

--=20
Jeff Mahoney
SUSE Labs


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