Hi,
On 5/21/2006 3:52 PM, Georger Araujo wrote:
I guess this means I'll have to closely watch how many
backups it takes to fill a tape - the worst case being
the nominal capacity of the tape, i.e. 200 GB
uncompressed. I deployed Bacula web-gui yesterday,
it'll make this task easier.
Try baculareport.pl, too...
I'm still puzzled, though, how BrightStor Enterprise
Backup 10.5 managed not only to estimate me how much
space was still available - it also told me the
compression ratio of the backup! I used to get 1.5:1
on Windows file servers and anything from 4:1 to 6:1
(!) on Oracle 8i. That was using an IBM 3583 LTO
Ultrium I tape library on Windows 2000 Advanced
Server.
Either it used software compression, or you can query the drive for the
compression ratio it achieved. (I doubt the latter, at least I don't
know any such drive... haven't investigated it, though.)
Using software compression, and limiting the tape capacity to a value
the software manufacturer determines allows that. (That's usualy the
case when you have a program where you have to set up the tape type in
my experience.) You can do the same with Bacula, by the way: Limit the
tape capacity to the value the technology sets. For example, Ultrium-1
would have a capacity of 10^9 bytes. The remaining capacity differences
between volumes would probably come from block size related overhead and
file marks - either live with it and hope the needed space can come from
the tapes "extra length" beyond the regularcapacity, or decrease the
fixed tape size by some percent.
Arno
Regards,
Georger
--- Arno Lehmann <[EMAIL PROTECTED]> escreveu:
Hmm. According to the documents I read, LOG SENSE
itself is optional,
and page 0x31 is vendor specific (according to SPC-3
draft, and SSC-3
draft, and assuming I understood the text
correctly). Instead, some data
is available in log page 0x0c, which is mandatory,
but there they only
talk about approximate values.
Only seeing what the standard calls "native
capacity" of a tape makes
one aware of the problems when trying to determine
tape capacity:
"3.1.43 native capacity: The capacity assuming
one-to-one compression
(e.g., compression disabled), the medium is in good
condition, and that
the device recommended typical block size is used."
Anyway, in typical scenarios, the only reliable way
way of guessing tape
capacity (or remaining capacity) is estimating based
on individual data,
i.e. using existing tapes with similar data on them
as reference.
Arno
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IT-Service Lehmann [EMAIL PROTECTED]
Arno Lehmann http://www.its-lehmann.de
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