zfs discuss - Jul 2009 - zfs: how is size of Volume computed?

hi,

  i''m using a zvol someone else created (and then used as
an iSCSI Target, via: "iscsitadm ... -b /dev/zvol ...").

I see that AVAIL has a size of 33GB, yet the VOLSIZE is 24GB ;

# zfs list -t volume -o name,avail,used,volsize iscsi-pool/log_1_1
NAME                AVAIL   USED  VOLSIZE
iscsi-pool/log_1_1  33.7G  24.4G    24.4G


I debugged ''format'', and it received a size of 24GB from
Sun''s
iSCSI Target implementation.  ''format'' did a READ-CAPACITY
(scsi)
cmd and was return "24GB".

why does 33GB show as AVAIL ?  should i be expecting 33GB''s worth
of usable disk space? ...or does AVAIL (for some weird reason also)
include metadata) ??

# zdb -v iscsi-pool/log_1_1
Dataset iscsi-pool/log_1_1 [ZVOL], ID 117, cr_txg 74, 54.0K, 3 objects

     Object  lvl   iblk   dblk  lsize  asize  type
          0    7    16K    16K    16K  14.0K  DMU dnode
          1    4    16K     8K  24.4G  38.0K  zvol object 
<<<<<<
          2    1    16K    512    512     1K  zvol prop


thanks
/andrew