Re: 5 _thousand_ snapshots? even 160?

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

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On 2014-10-21 21:10, Robert White wrote:
>
> I don't think balance will _ever_ move the contents of a read only
> snapshot. I could be wrong. I think you just end up with an endlessly
> fragmented storage space and balance has to take each chunk and search
> for someplace else it might better fit. Which explains why it took so long.
>
> And just _forget_ single-extent large files at that point.
>
> (Of course I could be wrong about the "never move" rule, but that would
> just make the checksums on the potentially hundreds or thousands of
> references need to be recalculated after a move, which would make
> incremental send/receive unfathomable.)
>
Balance doesn't do anything different for snapshots from what it does 
with regular data.  I think you are confusing balance with 
defragmentation, as that does (in theory) handle snapshots differently. 
  Balance just takes all of the blocks selected by the filters, and 
sends the through the block allocator again, and then updates the 
metadata to point to the new blocks.  It can result in some 
fragmentation, but usually only for files bigger than about 256M, and 
even then doesn't always cause fragmentation
>
> On 10/21/2014 01:44 PM, 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,
>>
>> 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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