Reducing ZFS fragmentation by copying to larger disk

[Mark Martinec]

>> 1. attach new disks to a ZFS mirror and let them resilver, ...
> 
> I don't think this would help with fragmentation at all.

Thank you for confirming my guess!


>> 2. use zfs send / receive to make a copy
> 
> [...] It will even work within the same pool if there is enough free 
> space.

Nice, this is helpful!

   Mark



2018-01-16 01:28, je Bob Friesenhahn wrote:

> On Tue, 16 Jan 2018, Mark Martinec wrote:
>> Having a ZFS filesystem with two 4 TB disks in a mirror that
>> is 85 % full and apparently pretty much fragmented (scrubs
>> or a resilver takes excessively long time), I intend to move
>> its contents to a new pair of disks twice the size.
>> 
>> My question is what method to use so that in the end the copy will
>> be less fragmented:
>> 
>> 1. attach new disks to a ZFS mirror and let them resilver, then
>>   remove the old disks (Would the copied content be any less
>>   fragmented, or perhaps would the added free space just
>>   relieve some of the problem?)
> 
> I don't think this would help with fragmentation at all.
> 
>> 2. use zfs send / receive to make a copy
>>   (is this any better than method #1 ?)
> 
> This will work well as long as there is enough space to send to.  It
> will even work within the same pool if there is enough free space.
> 
> Bob