topic Re: Which tape device do I use ? in Operating System - HP-UX

Which tape device do I use ?

SuperDome_1 — Tue, 27 May 2003 12:45:22 GMT

Hi.. I'm trying to backup several directories of varying sizes to tape (a DDS-3 with 12 Gb native and 24 Gb compressed capacity)

I run ioscan -fnC tape to determine the device and get the following output :

Class I H/W Path Driver S/W State H/W Type Description
=======================================================================
tape 0 0/0/0/3/1.3.0 stape CLAIMED DEVICE HP C1537A
/dev/rmt/0m
/dev/rmt/0mb
/dev/rmt/0mn
/dev/rmt/0mnb
/dev/rmt/c3t3d0BEST
/dev/rmt/c3t3d0BESTb
/dev/rmt/c3t3d0BESTn
/dev/rmt/c3t3d0BESTnb
/dev/rmt/c3t3d0DDS
/dev/rmt/c3t3d0DDSb
/dev/rmt/c3t3d0DDSn
/dev/rmt/c3t3d0DDSnb

My question is, which tape device do I use with the tar cvf command, and also is there a particular device I should use if I want to put 24 Gb of data on this tape, (or do I have to compress the data first)..

Thx

Re: Which tape device do I use ?

Ross Zubritski — Tue, 27 May 2003 12:47:13 GMT

/dev/rmt/0mnb

Re: Which tape device do I use ?

Uday_S_Ankolekar — Tue, 27 May 2003 12:49:04 GMT

ou can use /dev/rmt/0m or /dev/rmt/0mn

If it's the only drive then system will take it as default drive ( I mean no need to specify which device)

tar -cv will capture appropriate drive!

-USA..

Re: Which tape device do I use ?

Uday_S_Ankolekar — Tue, 27 May 2003 12:49:28 GMT

You can use /dev/rmt/0m or /dev/rmt/0mn

If it's the only drive then system will take it as default drive ( I mean no need to specify which device)

tar -cv will capture appropriate drive!

-USA..

Re: Which tape device do I use ?

Helen French — Tue, 27 May 2003 12:51:10 GMT

I would use this command for normal tar backup (no compression):

# tar -cvf /dev/rmt/0m
OR
# tar -cvf /dev/rmt/0mn (for no rewind)

If I need compressed (24GB), I would use:
# tar -cvf /dev/rmt/c3t3d0BEST
OR
# tar -cvf /dev/rmt/c3t3d0BESTn (for no rewind)

Re: Which tape device do I use ?

Pete Randall — Tue, 27 May 2003 12:51:57 GMT

I would choose
/dev/rmt/c3t3d0BEST, which will select the best available density. And I don't think you want a no-rewind device (nor a berkely style).

Pete

Re: Which tape device do I use ?

James R. Ferguson — Tue, 27 May 2003 12:59:50 GMT

Hi:

For compression, when the tape drive supports it, use a device with "best" or a device file linked to one. Actually, this should be any of the '0m' files.

To see the attributes associated with a device file, do:

# lssf /dev/rmt/filename

For a complete picture of tape devices, see the 'mt(7)' man pages.

Regards!

...JRF...

Re: Which tape device do I use ?

Paula J Frazer-Campbell — Tue, 27 May 2003 13:01:35 GMT

Hi

Info on tape device files:-

http://docs.hp.com/cgi-bin/fsearch/framedisplay?top=/hpux/onlinedocs/B2355-90053/B2355-90053_top.html&con=/hpux/onlinedocs/B2355-90053/00/00/42-con.html&toc=/hpux/onlinedocs/B2355-90053/00/00/42-toc.html&searchterms=insf&queryid=20030527-075959

Paula

Re: Which tape device do I use ?

Jean-Louis Phelix — Tue, 27 May 2003 13:03:30 GMT

hi,

I would always use /dev/rmt/Om. In fact it's always a hard link to the corresponding 'BEST DENSITY' file :

hp> ll /dev/rmt
total 12
drwxr-xr-x 2 bin bin 1024 Dec 19 15:22 .
dr-xr-xr-x 20 bin bin 5120 May 26 11:29 ..
crw-rw-rw- 2 bin bin 205 0x000000 Jan 23 15:09 0m
crw-rw-rw- 2 bin bin 205 0x000080 Dec 19 15:22 0mb
crw-rw-rw- 2 bin bin 205 0x000040 Jan 8 11:08 0mn
crw-rw-rw- 2 bin bin 205 0x0000c0 Dec 19 15:22 0mnb
crw-rw-rw- 2 bin bin 205 0x000000 Jan 23 15:09 c0t0d0BEST
crw-rw-rw- 2 bin bin 205 0x000080 Dec 19 15:22 c0t0d0BESTb
crw-rw-rw- 2 bin bin 205 0x000040 Jan 8 11:08 c0t0d0BESTn
crw-rw-rw- 2 bin bin 205 0x0000c0 Dec 19 15:22 c0t0d0BESTnb
crw-rw-rw- 1 bin bin 205 0x000001 Dec 19 15:22 c0t0d0DDS
crw-rw-rw- 1 bin bin 205 0x000081 Dec 19 15:22 c0t0d0DDSb
crw-rw-rw- 1 bin bin 205 0x000041 Dec 19 15:22 c0t0d0DDSn
crw-rw-rw- 1 bin bin 205 0x0000c1 Dec 19 15:22 c0t0d0DDSnb

Regards.

Re: Which tape device do I use ?

Paula J Frazer-Campbell — Tue, 27 May 2003 13:06:01 GMT

Hi

Also

The tape device names have the following format:-

/dev/rmt/#dbn

where:-

# --- Logical tape number
d -- Tape density (h,m,l)
b -- BSD behavior
n -- No-rewind

Paula

Re: Which tape device do I use ?

Pete Randall — Tue, 27 May 2003 13:10:47 GMT

Just an addendum to Jean-Louis suggestion:

Don't use /dev/rmt/Om (with a capital letter "o") - use /dev/rmt/0m (with a numeral "0"), otherwise you're likely to fill up your root file system.

Pete

Re: Which tape device do I use ?

SuperDome_1 — Tue, 27 May 2003 13:15:13 GMT

Thx for all your replies..

I've decided to take 2 backups , one using /dev/rmt/0mnb (since when I did a tar cvf /dev/rmt/0m, I was prompted for another tape, for the same directory) and the other using /dev/rmt/c3t3BEST0mnb.

I understand why I have to use norewind (to save tape space), but is there any other reason I should use norewind.

I'm also not sure why choosing a berkeley device (say /dev/rmt/0mnb) versus a non-berkeley (at&t) would matter.

I'm taking a tar on HP-UX 11.11, and will be restoring on to a system with HP-UX 11.0

Thx again for all your replies. Really appreciate it.. !!!

Re: Which tape device do I use ?

James R. Ferguson — Tue, 27 May 2003 13:56:55 GMT

Hi (again):

In answer to your last questions:

You would use a "no-rewind" device if you wanted to package, for instance, multiple tar archives on a single tape. Ignite 'make_tape_recovery' uses a no-rewind device so that the LIF file can be placed on the recovery tape followed by the 'pax' archive. Hence you see this sequence to extract a file from the 'pax' (or 'tar') archive:

# mt -t /dev/rmt/0mn fsf 1
# tar -xvf /dev/rmt/0m filename

With regard to AT&T versus Berkley, the 'mt(7)' man pages note: "...When a file open for reading (only) is closed and the no-rewind bit is not set, the tape is rewound. If the no-rewind bit is set, the behavior depends on the style mode. For AT&T-style devices, the tape is positioned after the EOF following the data just read (unless already at BOT or Filemark). For Berkeley-style devices, the tape is not repositioned in any way."

Regards!

...JRF...

Re: Which tape device do I use ?

Rajesh G. Ghone — Wed, 28 May 2003 09:46:10 GMT

Hi,

you just give #tar -cv this will automatically take the default device file(the default device file is 0m)I have told you not to give device file because i have your ioscan output & through that output only i can say not give any device file.

Regards,
Rajesh G.

Re: Which tape device do I use ?

Duncan Edmonstone — Wed, 28 May 2003 10:34:42 GMT

Incidentally, you'll be very lucky to get 24GB of data on a single tape. This is assuming the best available type of data to compress and works off a compression ratio of 2:1. A more realistic compression ratio for most data types is 1.4:1 or about 16-17GB. Of course if most of what you are backing up is pictures/movies etc which are already stored in fairly compressed formats then you won't even get that.

HTH

Duncan