Filesystems, Disks and Memory

I have been trying to backup my NetApp /vol/vol0 data to local tape drive. It is around 68GB.
The tape I am using is DLT tape and should be able to handle 70GB data. However, dump always
aborted around reaching 57~58GB data.
Tape drive is attached on NetApp.

1st try to dump /vol/vol0 to local drive (68GB) => dump aborted
2nd try to dump /vol/vol0/home to local tape drive (59GB) =>dump aborted
Any idea?

Here are some info
==========================================
NetApp filer name: netmgtfs1

root@woodstock> uname -a
SunOS woodstock 5.6 Generic_105181-15 sun4u sparc SUNW,Ultra-2

root@woodstock> rsh netmgtfs1 "mt -f nrst0a status"
Tape drive: Digital DLT7000
Status: ready, write enabled
Format: 85937 bpi 70 GB (w/comp)
fileno = 0 blockno = 0 resid = 0

root@woodstock> rsh netmgtfs1 "df "
Filesystem kbytes used avail capacity Mounted on
/vol/vol0/ 69580432 66787380 2793052 96% /vol/vol0/
/vol/vol0/.snapshot 17395108 2353816 15041292 14% /vol/vol0/.snapshot

root@woodstock> mount -F nfs netmgtfs1:/vol/vol0 /mnt
root@woodstock> ls /mnt
PROBLEM090199/ heaven1_org@ nms/ sunroot/
etc/ home/
global2/ nmd/

root@woodstock> du -sk home
59049872

root@woodstock>!!
rsh netmgtfs1 "dump 0uf nrst0a /vol/vol0/home"

DUMP: creating "/vol/vol0/../snapshot_for_backup.201" snapshot.
DUMP: Using Partial Volume Dump
DUMP: Date of this level 0 dump: Sat May 4 00:39:57 2002.
DUMP: Date of last level 0 dump: the epoch.
DUMP: Dumping /vol/vol0/home to nrst0a
DUMP: mapping (Pass I)[regular files]
DUMP: mapping (Pass II)[directories]
DUMP: estimated 58520516 tape blocks.
DUMP: dumping (Pass III) [directories]
DUMP: dumping (Pass IV) [regular files]
DUMP: We have written 1785109 KB to tape.
DUMP: We have written 3613470 KB to tape.
DUMP: We have written 5714735 KB to tape.
DUMP: We have written 7939329 KB to tape.
.....
DUMP: We have written 53961774 KB to tape.
DUMP: We have written 55563549 KB to tape.
DUMP: We have written 57590637 KB to tape.
DUMP: DUMP IS ABORTED
DUMP: Deleting "/vol/vol0/../snapshot_for_backup.201" snapshot.

Try the following (and read the man page for the options):

Instead of
rsh netmgtfs1 "dump 0uf nrst0a /vol/vol0/home"

use
rsh netmgtfs1 "dump 0bcuf 126 nrst0a /vol/vol0/home"

The native capacity of a DLT7000 is 35Gb. With compression on you can get a theoretical 70Gb but in real life much less. Your figure of 57-58Gb sounds about right, although it does depend on what you're backing up and how well it can be compressed.