Re: Reasonable amount of snapshots

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2017年11月01日 19:31, ST wrote:
> On Wed, 2017-11-01 at 19:17 +0800, Qu Wenruo wrote:
>>
>> On 2017年11月01日 19:04, ST wrote:
>>> Hello,
>>>
>>> I read in different places that one should keep amount of snapshots low
>>> - around 15-20. My question - is this limitation on total number of
>>> snapshots on the system or only on related (parent<->child) chain of
>>> snapshots?
>>
>> Independent subvolume doesn't count, and it's filesystem based.
>>
>> So only snapshots (with source exists, and still shares a lot of trees
>> with source) counts.
>>
>> And if you have multiple btrfs fses, then the count should be based on
>> each fs.
>>
>>> What I want to do is the following: create (and then rotate) last 7
>>> daily snapshots (and maybe 4 weekly) for each user in his /home dir.
>>> For
>>> around 100 users. So if limitation is only on related snapshots then I'm
>>> OK since only each 7 (or maybe 7+4) of them are related which is well
>>> under the 15-20 limit. However in total there could be 700 snapshots. So
>>> what is true?
>>
>> You're OK since independent subvolumes won't cause too much stress for
>> backref walk.
>>
>> The only thing you may need to consider is to limit the ability to
>> reflink data between subvolumes.
>> Like cp --reflink or even offline dedupe.
> 
> Thank you very much! How can I limit this ability? (I'm on Debian9)
> 
> All the best!

No way to limit, unfortunately.

Thanks,
Qu


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