[H-GEN] Tape backup from Linux to Sun

[James C. McPherson]

(Note reply-to: being general at humbug.org.au vs "James C. McPherson" <James.McPherson at mq.edu.au>)


Rob Irvine writes:
 > (Note reply-to: being general at humbug.org.au vs Rob Irvine <robi at hastdeer.com.au>)
 >   I am trying to do a tape backup from a Linux Redhat 5.2 Intel disk to
 > a Sun Sparc Solaris7 8mm Exabyte tape drive.
 > 
 >  I use the following command on Linux
 > 
 >  /sbin/dump 0fu sunipaddress:/dev/rmt/0 /dev/hda2
 > 
 >  This is working (I think, although I have not tried a restore yet) but
 > my problem  is that it appears to need 30 tapes to do  the backup when I
 > only have about 1Gb of data to copy and the Exa tape is  apparently
 > capable of backing up to 14Gb compressed.  I though it might have
 > something to do with differences between Solaris and Linux tape density
 > or length defaults and accordingly  have tried setting  the density to
 > 6250 with a "d6250" arg but Linux doesn't like this and also  tried
 > using /dev/rmt/0c assuming "c" is to compress the data.
 > 
 >  None of this makes any difference that I can see.
 >  The Sun is a ufs system and the Linux is ext2.


ok. What you need to know about exabytes: on solaris (and possibly other sysv
unices): if you use /dev/rmt/0 then you will get the lowest common denominator 
data density. You should be using the compressed non-rewinding device on the
sun - /dev/rmt/0cn - because you'll get better writes and the likelihood that
you will actually get closer to the alleged 14Gb capacity of the tape. (I say
"alleged" because (1) sun refuse to guarantee that any tape will give you more 
than 2Gb - even DLT7000s; (2) 14Gb requires at least 2:1 compression for _all_ 
the files/data being dumped, which is so totally unlikely, and (3) you never,
ever, ever believe the tape drive vendor's stated maximum capacity if you want 
to avoid being badly burnt). 

I would suggest that you also add a blocksize option to your dump command:


/sbin/dump 0bfu 126 sun:/dev/rmt/0cn files_to_dump


and that instead of dumping the raw device (unless you've umounted it and
basically gone to single-user) you instead dump the partition (eg, /usr or
/opt) because it works just as well.

If you screw around with making dump pass a density to the drive you will
definitely waste your tapes, since solaris has enough smarts built in to it to 
be able to figure out what density to use. The Exabyte drivers are so popular
that Sun includes them as part of its default "st" driver - you can be pretty
darn sure that by now they've got it right.

As for the "taking 30 tapes" thing - are there any logfile messages or output
from dump which you could forward to me/the list so we can see more precisely
what's happening?


James C. McPherson
--
Unix Systems Administrator            Phone: +61.2.9850.9418
Office of Computing Services            Fax: +61.2.9850.7433
Macquarie University   NSW    2109     
AUSTRALIA			     

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