Am 01.12.2016 um 16:48 schrieb Chris Murphy:
> On Thu, Dec 1, 2016 at 7:10 AM, Stefan Priebe - Profihost AG
> <s.pri...@profihost.ag> wrote:
>>
>> Am 01.12.2016 um 14:51 schrieb Hans van Kranenburg:
>>> On 12/01/2016 09:12 AM, Andrei Borzenkov wrote:
>>>> On Thu, Dec 1, 2016 at 10:49 AM, Stefan Priebe - Profihost AG
>>>> <s.pri...@profihost.ag> wrote:
>>>> ...
>>>>>
>>>>> Custom 4.4 kernel with patches up to 4.10. But i already tried 4.9-rc7
>>>>> which does the same.
>>>>>
>>>>>
>>>>>>> # btrfs filesystem show /ssddisk/
>>>>>>> Label: none  uuid: a69d2e90-c2ca-4589-9876-234446868adc
>>>>>>>         Total devices 1 FS bytes used 305.67GiB
>>>>>>>         devid    1 size 500.00GiB used 500.00GiB path /dev/vdb1
>>>>>>>
>>>>>>> # btrfs filesystem usage /ssddisk/
>>>>>>> Overall:
>>>>>>>     Device size:                 500.00GiB
>>>>>>>     Device allocated:            500.00GiB
>>>>>>>     Device unallocated:            1.05MiB
>>>>>>
>>>>>> Drive is actually fully allocated so if Btrfs needs to create a new
>>>>>> chunk right now, it can't. However,
>>>>>
>>>>> Yes but there's lot of free space:
>>>>>     Free (estimated):            193.46GiB      (min: 193.46GiB)
>>>>>
>>>>> How does this match?
>>>>>
>>>>>
>>>>>> All three chunk types have quite a bit of unused space in them, so
>>>>>> it's unclear why there's a no space left error.
>>>>>>
>>>>
>>>> I remember discussion that balance always tries to pre-allocate one
>>>> chunk in advance, and I believe there was patch to correct it but I am
>>>> not sure whether it was merged.
>>>
>>> http://www.spinics.net/lists/linux-btrfs/msg56772.html
>>
>> Thanks - still don't understand why that one is not upstream or why it
>> was reverted. Looks absolutely reasonable to me.
> 
> It is upstream and hasn't been reverted.
> 
> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/fs/btrfs/volumes.c?id=refs/tags/v4.8.11
> line 3650
> 
> I would try Duncan's idea of using just one filter and seeing what happens:
> 
> 'btrfs balance start -dusage=1 <mp>'

see below:

[zabbix-db ~]# btrfs balance start -dusage=1 /ssddisk/
Done, had to relocate 0 out of 505 chunks
[zabbix-db ~]# btrfs balance start -dusage=10 /ssddisk/
Done, had to relocate 0 out of 505 chunks
[zabbix-db ~]# btrfs balance start -musage=1 /ssddisk/
ERROR: error during balancing '/ssddisk/': No space left on device
There may be more info in syslog - try dmesg | tail
[zabbix-db ~]# dmesg
[78306.288834] BTRFS warning (device vdb1): no space to allocate a new
chunk for block group 839941881856
[78306.289197] BTRFS info (device vdb1): 1 enospc errors during balance

> 
> 
>>>>> With enospc debug it says:
>>>>> [39193.425682] BTRFS warning (device vdb1): no space to allocate a new
>>>>> chunk for block group 839941881856
>>>>> [39193.426033] BTRFS info (device vdb1): 1 enospc errors during balance
> 
> It might be nice if this stated what kind of chunk it's trying to allocate.
> 
> 
> 
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