Solaris

Dear Gurus,
I am experincing very slow backup on a DLT 8000 tape drive.
Knowing that the transfer rate of this tape is 6 MB/s, we have a write rate of 4 MB/s, no waits, average service time about 25 % and the disaster 99 % busy percentage.

uname -a
SunOS DCHQINTA1 5.9 Generic_118558-06 sun4u sparc SUNW,Sun-Fire-480R

iostat -xdnz 10 30:

extended device statistics
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
0.1 0.9 0.8 5.6 0.0 0.0 0.0 1.2 0 0 c4t1d0
0.0 2.1 0.0 10.0 0.0 0.0 0.0 0.7 0 0 c4t0d1
0.0 1.3 0.0 10.4 0.0 0.0 0.0 0.7 0 0 c4t0d3
36.2 0.2 3988.0 0.8 0.0 0.2 0.0 5.0 0 5 c4t1d2
0.0 5.0 0.0 31.1 0.0 0.0 0.0 6.8 0 2 c1t0d0
0.0 41.8 0.0 4012.8 0.0 1.0 0.0 23.8 0 99 rmt/0
extended device statistics
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
0.0 0.7 0.0 3.0 0.0 0.0 0.0 6.3 0 0 c4t1d0
0.0 1.7 0.0 7.6 0.0 0.0 0.0 0.5 0 0 c4t0d1
0.1 1.3 0.8 9.7 0.0 0.0 0.0 1.1 0 0 c4t0d3
37.2 0.1 4094.4 0.1 0.0 0.2 0.0 5.4 0 5 c4t1d2
0.0 16.6 0.0 123.9 0.0 0.2 0.0 9.5 0 9 c1t0d0
0.0 41.9 0.0 4022.4 0.0 1.0 0.0 23.7 0 99 rmt/0
extended device statistics
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
0.0 6.3 0.0 16.0 0.0 0.0 0.0 1.1 0 0 c4t1d0
0.0 2.1 0.0 7.8 0.0 0.0 0.0 0.6 0 0 c4t0d1
0.0 1.8 0.0 13.0 0.0 0.0 0.0 0.7 0 0 c4t0d3
35.8 0.0 3987.2 0.0 0.0 0.2 0.0 5.3 0 4 c4t1d2
0.0 0.7 0.0 1.9 0.0 0.0 0.0 11.0 0 0 c1t0d0
0.0 41.7 0.0 4003.2 0.0 1.0 0.0 23.8 0 99 rmt/0

Any advice, why am i having 99 % busy percentage ?

I dun really trust the %b. You should be doing fine for 4MB out of 6MB