Adding SUN DLT7000 to 9000/800/rp7420 running 11.11

[Unix Team]

We have added the only existing DLT drive we can find to copy off some user data. We are trying to get the tape to write compressed using the 70Gbs available on this TYPE IV tape.

This is the Solaris command that we were given...
# dd if=/ccd/path/path_XXX.dat obs=32538 cbs=638 conv=ebcdic of=/dev/rmt/0un &

mt -t /dev/rmt/0un eof 10

What is the HP equivilant of the 'u' switch? 0mn gives us 40gb.

[A. Clay Stephenson · Accepted solution]

There is no equivalent since the "mn" is using the 'BEST' device settings, it is as compressed as it's going to get.

Bear in mind that the 70GiB value assumes a 2:1 compression ratio but that is purely data dependent. The compression is done on the drive itself so that the only thing that the host computer does is requests that compression be enabled. You device node already does that although you should be able to manually set the compression from the front panel of the drive. The native capacity of a DLT IV tape is 35GiB -- that is all that you can absolutely, positively count on. Since you are getting 40GiB, your data are being compressed --- just nowhere near the "marketing" 2:1 ratio.

I have seen these same drives store over 100GiB of data and I've also seen them reach EOT at just over 35GiB; it all depends upon the data.

[A. Clay Stephenson]

One thing that I should add is that you are specifying an 'n' (norewind) device so you could get less than even 35GiB unless you actually start at the beginning of the media. Since I saw an EBCDIC conversion, I assumed that you were actually writing label/header data first and then the actual data file but that was an assumption. You can simpply use the 'm' device node to always rewinds or use the mt command to rewind the tape.