ExaByte Dump commands

[David Collins]

In article <10542 at batcomputer.tn.cornell.edu> rogerj at tcgould.tn.cornell.edu (Roger Jagoda) writes:
>Folks,
> 
>I have inherited a UNIX system (VAX/ULTRIX) with a SCSI Exabyte (OEM'd 3rd Party as usual) Tape unit. My question regards the parameters for the best "dump"
>command use. For example, we're using now:
> 
>dump <level>usdf 4800 6666 /dev/nrmt1h <f. system>
> 
>This assumes a density or 4800 and a tape length of 6666 feet which CAN't
>be correct. Something is wrong as we can't restore files either..:-( 
> 
>The tape unit responds with "not a dump tape, I/O error"
> 
>So, the tapes are SONY 120Ps and the ExaByte manual says the drive is capable
>of writing "linear recording density = 43200 bits/inch"
> 
>Now, isn't this the number we should use instead of 4800 (which sounds more 
>like a guess from the old 1600 bpi tape reel days..)?
> 
>As for feet of tape length, we have asked everyone including the mail
>order house where the tapes were bought, NO ONE seesm to know how many
>feet of tape come on a 120 tape! The actual model number of the tape is
>"P6-120MP" for "Metal Particle". If anyone knows how long these tapes
>are can they post an answer? Thanks. Actually, couldn't we just put a
>very large number for the lenght (like 100000)? That number is just
>so the tape doesn't run off the reel during the dump, right? Well, our
>dumps don't take up 2.2G so there's probably no danger of that.
> 
>
>Should our dump command be more like:
> 
>dump <level>udsf 43200 100000 /dev/nrmt1h <f.system> ?
> 
>Thanks in advance for any pointers or comments!
> 
>--Roger Jagoda
>--Cornell University
>
>-- 
>-------------------------------------------------------------------------
>Roger Jagoda                          -- My employers don't even like paying
>Cornell University                         me, let alone accept responsibility
>fqoj at cornella.cit.cornell.edu              for anything I say or do! --



I think that you will find that the density that the exabyte simulates is
1600 and that if you are using the "90" minute tapes the length of the tape
is 116000 feet.  Those are the parameters (and tapes) that I use on our 
inhouse systems and I havent had a problem when needing to restore files 
"that disappeared".  If you want the equation to work out the length:

The 90 minutes (standard play) tape can hold over 2.0 gigabytes.
 
                     (Block size) * (Tape Length)
 0.95 * 2143303680 = ---------------------------- = Tape Capacity = 2036138496 
                           (Block size)
                           ------------ + 0.6
                               1600
 
 Where : Block size  = 2048 * 5 = 10k (default "dump" parameters)
         Tape length = the length of the tape in inches ("dump" requires feet).
         1600        = B.P.I. density emulated by the drive.
         0.6         = Inter record gap (inches).
 
The tape length calculated from this formula is 116000 ft.
The formula above originated from Mike Shrimpton at Interface Distributors Ltd
and as I stated above the results have served me alright. 
 
BTW If you are backing up across an ethernet a block size of 32 appears to
speed up the dumps on our inhouse systems.

Good Luck
 
      -m-------  Dave Collins                   email :     davec at uk.co.pyra
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