illumos gate

If you create a volume with the -b option, zfs will compute a higher than volsize value for refreservation to accommodate the extra meta data for the volume. If you change that value for refreservation, it can not be set back to it's original value. Zfs refuses any value greater than volsize.

Here is the problem happening on 151_a4:
root@csabastore:~# zfs get -pH volsize,volblocksize,refreservation test/one
test/one volsize 1073741824 local
test/one volblocksize 8192 -
test/one refreservation 1107820544 local
root@csabastore:~# zfs set refreservation=500M test/one
root@csabastore:~# zfs get -pH volsize,volblocksize,refreservation test/one
test/one volsize 1073741824 local
test/one volblocksize 8192 -
test/one refreservation 524288000 local
root@csabastore:~# zfs set refreservation=1107820544 test/one
cannot set property for 'test/one': 'refreservation' is greater than current volume size

And here it is on S11:
root@kass:/home/tsoome# zfs create -V 1G data/test
root@kass:/home/tsoome# zfs get volsize,refreservation,usedbyrefreservation data/test
NAME PROPERTY VALUE SOURCE
data/test volsize 1G local
data/test refreservation 1,03G local
data/test usedbyrefreservation 1,03G -
root@kass:/home/tsoome# zfs set refreservation=500MB data/test
root@kass:/home/tsoome# zfs get volsize,refreservation,usedbyrefreservation data/test
NAME PROPERTY VALUE SOURCE
data/test volsize 1G local
data/test refreservation 500M local
data/test usedbyrefreservation 500M -
root@kass:/home/tsoome# zfs set refreservation=1G data/testroot@kass:/home/tsoome# zfs get volsize,refreservation,usedbyrefreservation data/test
NAME PROPERTY VALUE SOURCE
data/test volsize 1G local
data/test refreservation 1G local
data/test usedbyrefreservation 1024M -
root@kass:/home/tsoome# zfs set refreservation=1,03G data/testcannot set property for 'data/test': 'refreservation' is greater than current volume size