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I've move a zfs filesystem from a pool made of a bunch or mirror vdevs to another pool made of two raidz1s with the following command

# zfs send -R pool/project@moving | zfs recv tank/project

As far as I understood the manpage, '-R' moves all the metadata as well, including the compression algorithm etc., which is exactly what I see:

# zfs get compression pool/project
pool/project    compression  lz4       local
# zfs get compression tank/project
tank/project    compression  lz4       received

So why is the the filesystem on the target pool (tank) over 20% bigger than on the source pool (pool). It's a diference of almost 6TB and I'm curious, where I lost that.

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Show the filesystem sizes, please... zfs list – ewwhite Jul 21 '14 at 11:30
Oh, you're right, 'zfs list' show actually the same size. But why does 'zpool list' show this: # zpool list NAME SIZE ALLOC FREE EXPANDSZ CAP DEDUP HEALTH ALTROOT pool 36.2T 27.9T 8.33T - 77% 1.00x ONLINE - tank 36.2T 34.7T 1.57T - 95% 1.00x ONLINE - – Clayton Louden Jul 21 '14 at 11:57
Curious. Why are you moving to RAIDZ? – ewwhite Jul 21 '14 at 12:44
up vote 1 down vote accepted

ZFS mirrors are usually much better than RAIDZ(1/2/3) for a variety of reasons (performance, expansion, sanity). This confusion about displayed size is one of them.

Please see: Why is my RAIDZ2 pool larger than the expected size calculation?

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