zfs create -o volblocksize doesn't refreserve enough
CR6429996, zvols don't reserve enough space for requisite meta data
was integrated into ON b132. If a zvol is created using the "zfs -b blocksize"
option, then zfs_add_synthetic_resv() is called to increase the refreservation
to accomodate metadata needs as the pool fills.
However, if the file system is created using the "zfs -o volblocksize=XXX"
option, then zfs_add_synthetic_resv() is not called and the refreservation
is set to the same size as the zvol (volsize). In other words, the fix for
CR6429996 does not cover this case.
Workaround: use -b option to set blocksize when creating zvols.
For more discussion, see