Urgently need some help solving lost space due to snapshots during receive op

[Rick Romero]

  Quoting Da Rock <freebsd-fs at herveybayaustralia.com.au>:

> On 10/08/2015 18:42, Willem Jan Withagen wrote:
>> On 10-8-2015 06:42, Da Rock wrote:
>>> I'm trying to move a pool from one system to another - exact same hdd
>>> and config, different in other areas. Both register same space
>>> available, and so should be no issue. The old system is quite full -
>>> still at least 5% free though.
>>
>> Hi,
>>
>> Are the versions of your FreeBSD also equal?
>
> No. 9.1 to 10.1.
>> Because in newer version, the free space reservation is significantly
>> bigger. So if disks are equal size, then with newer FreeBSDs you have
>> less usable space available.
>> Don't know the exact SVN commit where it happened. But there are more
>> question on this topic in the list, and they all boil down to the same
>> thing: ZFS needs more reserved space to be able to do certain things
>> without freezing the system.
>>
>> I've not read any suggestions that you can circumvent this setting.
>
> Crap. So I guess my best will be to compress as best I can for the
> moment or something like that.
>> As a second note I think is is more or less general understanding that a
>> ZFS systeem needs a lot more space left free than 5% to actual be able
>> to perform.
>> Last number I remember as sensible maximum fill level is around 70%.
>> If you go over it, your system is going to be busy with ZFS bookkeeping
>> instead of data storage.
>
> Yeah, I noticed that. Something I'm working on... backlog of sorting
> activities really :) Once I'm done it'll drop to well below 50% I'd say.
>> (One of the things I remember from the ZFS lecture by Kirk McKusik,
>> which I no longer can find on YouTube :( )
>>
>> --WjW
>
> Thanks for the info - I owe you a beer! At least I know why now and
> eases my growing headache from banging my head on the brick wall.

Also check out ashift.  I have hundreds of thousands of small files and
the ashift change ate up 25% additional space.

Rick