pid 81159 (bsdtar), uid 0 inumber 8 on /data: filesystem full

[freenas1]

hello all,
i have 8.3-RELEASE-p5 and about 590 datasets (homedirs). I got this error:

pid 66425 (bsdtar), uid 0 inumber 8 on /data: filesystem full

and /data is:

/dev/ufs/FreeNASs4 19M 10M 7.7M 58% /data

and i receive mails with subject:
Cron <root@freenas> /bin/sh /root/save_rrds.sh
containing:
tar: Write error

My questions are:
- is it possible to put /data on a zfs dataset?
- can i modify the script /root/save_rrds.sh to put rrd_dir.tar.bz2 where i have more place?

thanks in advance for help,

gerard