Re: btrfs-transacti hammering the system

["Austin S. Hemmelgarn" <ahferroin7@gmail.com>]

On 2017-12-01 16:50, Matt McKinnon wrote:
> Well, it's at zero now...
> 
> # btrfs fi df /export/
> Data, single: total=30.45TiB, used=30.25TiB
> System, DUP: total=32.00MiB, used=3.62MiB
> Metadata, DUP: total=66.50GiB, used=65.16GiB
> GlobalReserve, single: total=512.00MiB, used=0.00B
GlobalReserve seems to be used temporarily for certain cases of metadata 
COW regardless of how full the FS actually is, I'm betting that it just 
so happened that such a case was in progress when you got the info 
previously.  If you aren't seeing it regularly used, it's (probably) not 
an issue.

Duncan is correct though when dealing with long-term usage.  If you see 
GlobalReserve usage that persists for an extended period of time, 
something is almost certainly wrong, especially if the FS isn't close to 
being full.
> 
> 
> On 01/12/17 16:47, Duncan wrote:
>> Hans van Kranenburg posted on Fri, 01 Dec 2017 18:06:23 +0100 as
>> excerpted:
>>
>>> On 12/01/2017 05:31 PM, Matt McKinnon wrote:
>>>> Sorry, I missed your in-line reply:
>>>>
>>>>
>>>>> 2) How big is this filesystem? What does your `btrfs fi df
>>>>> /mountpoint` say?
>>>>>
>>>>
>>>> # btrfs fi df /export/
>>>> Data, single: total=30.45TiB, used=30.25TiB
>>>> System, DUP: total=32.00MiB, used=3.62MiB
>>>> Metadata, DUP: total=66.50GiB, used=65.08GiB
>>>> GlobalReserve, single: total=512.00MiB, used=53.69MiB
>>>
>>> Multi-TiB filesystem, check. total/used ratio looks healthy.
>>
>> Not so healthy, from here.  Data/metadata are healthy, yes,
>> but...
>>
>> Any usage at all of global reserve is a red flag indicating that
>> something in the filesystem thinks, or thought when it resorted
>> to global reserve, that space is running out.
>>
>> Global reserve usage doesn't really hint what the problem is,
>> but it's definitely a red flag that there /is/ a problem, and
>> it's easily overlooked, as it apparently was here.
>>
>> It's likely indication of a bug, possibly one of the ones fixed
>> right around 4.12/4.13.  I'll let the devs and better experts take
>> it from there, but I'd certainly be worried until global reserve
>> drops to zero usage.
>>