Re: Very slow balance / btrfs-transaction

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February 4, 2017 1:07 AM, "Goldwyn Rodrigues" <rgoldwyn@xxxxxxx> wrote:

> On 02/03/2017 06:30 PM, Jorg Bornschein wrote:
> 
>> February 3, 2017 11:26 PM, "Goldwyn Rodrigues" <rgoldwyn@xxxxxxxx> wrote:
>> 
>> Hi,
>> 
>> I'm currently running a balance (without any filters) on a 4 drives raid1 filesystem. The array
>> contains 3 3TB drives and one 6TB drive; I'm running the rebalance because the 6TB drive recently
>> replaced a 2TB drive.
>> 
>> I know that balance is not supposed to be a fast operation, but this one is now running for ~6 days
>> and it managed to balance ~18% (754 out of about 4250 chunks balanced (755 considered), 82% left)
>> -- so I expect it to take another ~4 weeks.
>> 
>> That seems excessively slow for ~8TiB of data.
>> 
>> Is this expected behavior? In case it's not: Is there anything I can do to help debug it?
>>> Do you have quotas enabled?
>> 
>> I might have activated it when playing with "snapper" -- I remember using some quota command
>> without knowing what it does.
>> 
>> How can I check its active? Shall I just disable it wit "btrfs quota disable"?
> 
> To check your quota limits:
> # btrfs qgroup show <mountpoint>
> 
> To disable
> # btrfs quota disable <mountpoint>
> 
> Yes, please check if disabling quotas makes a difference in execution
> time of btrfs balance.


Quata support was indeed active -- and it warned me that the qroup data was inconsistent. 

Disabling quotas had an immediate impact on balance throughput -- it's *much* faster now! 
>From a quick glance at iostat I would guess it's at least a factor 100 faster.


Should quota support generally be disabled during balances? Or did I somehow push my fs into a weired state where it triggered a slow-path?



Thanks!   
   
   j
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