Re: device balance times

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

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On 2014-10-21 16:44, Arnaud Kapp wrote:
> Hello,
>
> I would like to ask if the balance time is related to the number of
> snapshot or if this is related only to data (or both).
>
> I currently have about 4TB of data and around 5k snapshots. I'm thinking
> of going raid1 instead of single. From the numbers I see this seems
> totally impossible as it would take *way* too long.
>
> Would destroying snapshots (those are hourly snapshots to prevent stupid
> error to happens, like `rm my_important_file`) help?
>
> Should I reconsider moving to raid1 because of the time it would take?
>
> Sorry if I'm somehow hijacking this thread, but it seemed related :)
>
> Thanks,
>
The issue is the snapshots, because I regularly fully re-balance my home 
directory on my desktop which is ~150GB on a BTRFS raid10 setup with 
only 3 or 4 snapshots (I only do daily snapshots, cause anything I need 
finer granularity on I have under git), and that takes only about 2 or 3 
hours depending on how many empty chunks I have.

I would remove the snapshots, and also start keeping fewer of them (5k 
hourly snapshots is more than six months worth of file versions), and 
then run the balance.  I would also suggest converting data by itself 
first, and then converting metadata, as converting data chunks will 
require re-writing large parts of the metadata.
> On 10/21/2014 10:14 PM, Piotr Pawłow wrote:
>> On 21.10.2014 20:59, Tomasz Chmielewski wrote:
>>> FYI - after a failed disk and replacing it I've run a balance; it took
>>> almost 3 weeks to complete, for 120 GBs of data:
>>
>> Looks normal to me. Last time I started a balance after adding 6th
>> device to my FS, it took 4 days to move 25GBs of data. Some chunks took
>> 20 hours to move. I currently have 156 snapshots on this FS (nightly
>> rsync backups).
>>
>> I think it is so slow, because it's disassembling chunks piece by piece
>> and stuffing these pieces elsewhere, instead of moving chunks as a
>> whole. If you have a lot of little pieces (as I do), it will take a
>> while...
>>
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