Hi,
This morning I asked :
We have a 90M TLZ06 tape. As far as I know its capasity is ~3GB. I want
to increase this amount by compressing using -C and made a script like
mt -f /dev/rmt0h rew
vdump -0uCvf /dev/nrmt0h /
vdump -0uCvf /dev/nrmt0h /usr
vdump -0uCvf /dev/nrmt0h /root2
vdump -0uCvf /dev/nrmt0h /usr/local
vdump -0uCvf /dev/nrmt0h /usr/users/staff
vdump -0uCvf /dev/nrmt0h -D /usr/users/comp
vdump -0uCvf /dev/nrmt0h -D /usr/users/student
vdump -0uCvf /dev/nrmt0h -D /usr/users/academic
vdump -0uCvf /dev/nrmt0h -D /usr/users/others
vdump -0uCvf /dev/nrmt0h -D /usr/users/personel
mt -f /dev/nrmt0h weof
But, aproximately (but I'm not sure exactly, may be less than that ) after
3GB dump. it requires second tape ! But by comression it should dump
about 6GB , I think. Do you have any idea ?
Sincerely.
murat.
-- o --
Thanx to :
Lukas Rosenthaler <rosenth_at_foto.chemie.unibas.ch>
Olle Eriksson <olle_at_cb.uu.se>
Rainer Landes <rlandes_at_fphws01.physik.uni-karlsruhe.de>
iwm_at_uvo.dec.com
Peter Stern <peter_at_wiscpa.weizmann.ac.il>
Hellebo Knut <Knut.Hellebo_at_nho.hydro.com>
-- o --
Lukas Rosenthaler said :
The TLZ07 tape does already hardwarecompression - therefore it has a
capacity - depending on the data type - between 2 and 4 GB. If You do
a software compression, the tape hardware will not be able to compress
further, so You don't gain anything - up to the contrary: Compressing
already compressed files may *increase* the size of the "compressed" file.
-- o -
Olle Eriksson said :
With a tlz06 you select compress with the device name i. e. rmt0h
enables hardware compress rmt0l don't. Any additional compress will
not gain anything.
All sizes with compress are very approximate since you never can
tell how much you gain in the compression, that is data dependent.
You can not be sure that 3GB fits on the tape, you only knows that
3GB is an approximate number.
-- o --
Rainer Landes said :
My "Owners's manual" for the TLZ06 Tape says on page 1-1:
Tape Type No Compression Compression
60m 1.3GB 2.6GB
90m 2.0GB 4.0GB(typical)
You had 3GB on a 90m Tape. This means it is already compressed.
The compression factor depends on the type of data, I think.
So, with your kind of data you seem to get only 3GB, not 4GB as
was written in the manual.
-- o --
and iwm_at_uvo.dec.com said :
Unfortunately this is not an easy one to answer.
Tape capacities are normally theoretical, IF you can stream data to the
tape
at such a rate that it can keep running at it's top speed you could get
around
4 Gig compressed (TLZ06). However, depending on whether your data is lots
of
little files, or if the system was Vvery busy, or any one of a few other
reasons
then you won't hit that.
Incidentally, you should not need to use -C on vdump, the TLZ06 should
hardware
compress, which is alot faster than allowing vdump to do it. In fact
having the
software compress, may well mean that you are actually losing capacity,
since
you cannot double compress!
Perhaps the filesystem order might help?
-- o --
Peter Stern said :
I don't know where you got that. The capacity of a 90m TLZ06 DAT tape
is 2.0 Gbytes raw or 4.0 Gbytes assuming a 2x data compression. This
latter number is obviously only an estimate which depends very much on
the data you are compressing. In your case, it souns like you got more
like about 1.5x data compression.
-- o --
and Hellebo Knut said :
You have to use 120m tape.
-- o --
Thax for all.
Sincerely.
murat.
----
Murat Balci UNIX sys. Admin http://bornova.ege.edu.tr/~balci
s-mail : Ege Universitesi B.A.U.M - Bornova, IZMIR, TURKIYE.
e-mail : balci_at_bornova.ege.edu.tr Phone :+(90)(232)3881080-253
Received on Thu Mar 28 1996 - 14:37:55 NZST