Dear managers,
a few days ago I posted :
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Dear managers,
We have a couple of 4 gig drives and a TLZ07 tapestreamer. I am quite
confused about the capacity of this tape:
colle_at_krtkg4> file /dev/nrmt0h:
/dev/nrmt0h: character special (9/3) SCSI #0 TLZ07 tape #0 (SCSI ID
#0) errors = 0/6 61000_bpi
The tapes we are using are 90m(=90m x 100cm/m x 1/2.54(cm/inch) = 3543 inch
Using a density of 61000 bpi (bits per inch I presume) results in :
3543 inch x 61000 bits/inch x 1/8 bytes/inch = 26992500 bytes
This means I could backup only 26 Megabytes on this tape. When dumping a
backup to the same tape I can backup more as 2 Gigs, but less 3 Gigs.
My question are quite simple (I hope the answers will be as simple :-)
1) What is wrong in the calculation of the capacity ?
2) I was told that we could dump much more on this tape. Is this true,
and is my system badly configured, or is 2 Gigabyte the maximum capacity
of a 90m tape on a TLZ07 tapestreamer?
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Many thanks to:
alan_at_nabeth.cxo.dec.com who says:
The listed capacity of the TLZ07 using 120m tapes and
2:1 compression is 8 GB. Assuming no compression, then
with 120m tape it should support 4. Reducing the tape
length for 90m should be about 3 GB. 2 GB does seem
low, but it depends on how well the data compresses
and how much streaming and error handling is being done.
Older streaming tape drives didn't have much cache to
store data in order to keep the drive streaming. The
affect was a significant amount of start-stop which
reduced the tape capacity. Your tape is getting some
hard error (that 0/6 part of the file(1) output), so that
could reduce the capacity further.
GRANDLE_at_acodbob.larc.nasa.gov who says:
The actual linear density is 61000 bits/inch, however the tape uses
a hexical scan head. So the linear length of tape that the head sees
is much greater than the 90 meters. Without compression turned on
the tape can store about 2 gigabytes. With compression turned on
and depending on the type of data being written to the tape and how
it is written, you can get up to 6 Gigas to a tape. Typically I see
about 3.5 Gigs to a tape with dump.
and all the others who replied:
"Dr. Tom Blinn, 603-881-0646" <tpb_at_zk3.dec.com>, who sent me the product
description for the drive from the Systems and Options catalog
Brian Sherwood <sherwood_at_esu.edu>
Jim Belonis <belonis_at_dirac.phys.washington.edu>
fje_at_buckeye.cb.att.com
Olle Eriksson <olle_at_cb.uu.se>
Jon Buchanan <Jonathan.Buchanan_at_ska.com>
This mailing list a good thing(tm)
Christophe Colle
| \ =============================================================
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+---- mail: colle_at_krtkg1.rug.ac.be
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----------+ When I'm not in Ghent, Then I'm probably Sailing
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Received on Wed Mar 27 1996 - 15:31:06 NZST