UNIX for Advanced & Expert Users

My question is how much can you actually backup to a 160m tape and a 112m tape? i am trying to split all files and directories to it own section and what i am trying to do is find out much megabytes can each tape store so i know which tape to use.

It is impossible to say. The reason - different drives use different compression (as does software). One day you might put 2GB on a tape, the next day, 4GB. It matters on what you tell the system to use to do the backup (ufsdump, dd, tar, 3rd party backup software, ...) and what kind of compression the tape drive has. You might get a closer (ballpark) figure if you had posted the OS, backup software being used, and hardware make/model of the tape drive.

Example:

What tape device address do I use for for my 4mm(DAT) or my
8mm drive?

The answer is not generic and requires explanation....so:

>>>>>> 4mm Cartridge Storage Capacity* <<<<<<<<<<

Tape Lgth Low Density High Density
(/dev/rmt/0l) (/dev/rmt/0m, 0h, or 0c)

60 Meters 1.3 Gbyte 3.25 Gbyte*
90 Meters 2.0 Gbyte 5.0 Gbyte*


* High density mode uses the data compression capability of the drive.
Compression will vary depending on the type of data stored; typical
compression is 2.5:1.

>>>>>> 8mm Cartridge Storage Capacity and device name to use* <<<<<<<<<<

Scaling this down appropriately, for the 14GB and 160m tapes (and 2.3):
/dev/rmt/0l - ~3.5GB (uncompressed 8200 mode)
/dev/rmt/0m - ~7GB (uncompressed 8500 mode)
/dev/rmt/0h - ~7GB (uncompressed 8500 mode)
/dev/rmt/0c - 14GB (compressed 8500 mode)

Scaling this down appropriately, for the 14GB and 160m tapes (and 2.4):
/dev/rmt/0l - ~3.5GB (uncompressed 8200 mode)
/dev/rmt/0m - ~7GB (uncompressed 8500 mode)
/dev/rmt/0h - 14GB (compressed 8500 mode)
/dev/rmt/0c - 14GB (compressed 8500 mode)

* For ALL tape devices, YOU DO NOT need to use l,m,h, or "c" to get
maximum storage capacity on your tape. The device driver will use the
highest capacity mode avail for the tape drive being used. Bottom line,
Keep It Simple and suggest /dev/rmt/0 or /dev/rmt/0n (no-rewind) for
normal operations. Use the l,m,h or c for portability between respective
tape devices.


And:

What are the dump parameters for 4mm DAT drive for 4.1.3U1?

Here are the dump parameters for 4.1.3U1.

Native (non-compressed) mode:

dump 0ubdsf 96 54000 5200 /dev/rst0 /dev/xxx

The 96 specifies a blocking factor of 48 which is optimum for DAT/Loader
The 54,000 is the same density factor used for the 8mm drives
The 5,200 is used for size instead of 6000, because the DAT has a
capacity of 2GB rather than the 2.3GB capacity of 8mm drives.
The rst0 specifies non compression mode (this is very important)

compression mode:

The DAT drive supports compression. However, it is not possible to
determine how much data will fit on a tape. A typical value is twice
non-compression mode, but in some cases the data won't fit on the
tape and in many cases the data is muchmore compressible and tape
capacity will be wasted.

To be on the safe side, doubling the capacity is recommended. It should
be noted however that in some cases even this may not be conservative
enough, and that the only way to guarantee that the dump will not run
out of tape is to not use compression.

Doubling the size option (5200 in non-compressed mode) results in the
following command:

dump 0ubdsf 96 54000 10400 /dev/rst8 /dev/xxx

The 10400 specifies an anticipated capacity of 4Gbytes. Note the
use of /dev/rst8 instead of /dev/rst0.

If I have an 8mm tape drive using a 160m tape on Solaris 8, what are the ufsdump parameters and which device driver should I use to get the proper compression to tape? I think I need to use the /dev/rmt/0hn to get maximum compression or the /dev/rmt/0mn to get moderate compression. Correct?

The 8mm tape driver will always give you the max capacity. It ignores the bits in the minor number pertaining to density. However c indicates compressed and that is the max for drivers that care. Do a "man -s7i mtio" for the full list.

Sun's official recommendation is to use /dev/rmt/0 or /dev/rmt/0n or whatever. If you do a: "ls -lL /dev/rmt/0*" and look at the minor numbers, you will see that /dev/rmt/0 and /dev/rmt/0c are the same thing.

With every tape drive that I have ever seen, compression is either on or off. I don't believe that any tape drive will allow you to request different levels of compression.

thanks