Dumping to an exabyte tape drive

[Robert Scott]

In article <877 at iiasa.UUCP>, wnp at iiasa.AT (wolf paul) writes:
> In article <1990Sep1.143812 at suned1.nswses.navy.mil> jht at suned1.nswses.navy.mil (Jim Tibbs) writes:
> 
>	Stuff deleted.
> 
> These figures seem quite inconsisten. Which is correct?
> Would someone at SUN care to comment, ideally the person who wrote
> their drivers?
> 
> A Standard Tape has a density of  6250 bpi and a length of  2300 feet
> 
> Jim Tibbs specifies a density of 43000 bpi and a length of 12000 feet
> 
> Derick Linegar specifies       4100000 bpi and a length of  5190 feet
> 
> Frank Bresz specifies density of 54000 bpi and a length of  6000 feet
> 
> -- 

These numbers are really only used by the DUMP program to determine length of
tape for volume and "time to finish" estimates.  The actual device driver
will correctly write to the device regardless of what you specify in DUMP,
but the dump parameters affect how much of the tape you actually use.

We are using a Delta Microsystems driver here on Sun OS 4.01.  I quote from
the Delta Microsystems SS-2000T User's Guide (attributed, but not used by
permission):
	Using dump with a 2000T drive is essentially the same as using dump
	with any other tape device, except that you get a lot more information
	on each tape.  Because of the difference in bit density between the
	2000T and a normal 9-track drive, and because dump uses the 9-track
	drive as its reference in calculating the tape length, the tape length
	you provide for the 2000T must be the effective tape length (as if
	it were a 1600 bpi 9-track tape capable of storing the same number of
	megabytes as the 2000T tape).

	Formula for computing the tape length parameter:

		size = (((512*blocking factor)+1920)/blocking factor) * 
			((total Kbytes on tape - 2048)/10667)

	The blocking factor is how many 512 byte buffers (the standard
	buffer size for dump) should be used in 1 tape record (which
	by default is 1024 bytes for Delta).  So BF is 2,4,6... (default
	of 2).  Optimum for Delta is BF=124, or 62 Kbytes/block.  Total
	kbytes per tape is straight from a table as follows (for Sony
	P6 tapes, for domestic U.S.):

		15 minute tape:		258 Meg
		30 minute tape:		516 Meg
		60 minute tape:		1032 Meg
		etc....
	
	Example for a full dump command to a Sony P6-120 tape using
	optimal block size:
		dump 0fbs /dev/device_name 124 103400 partition_name


Hope this helps.

Zeke



-- 
~~~~~~~~~~~ From the Shrine of the "Last Gasp of ETA Systems" ~~~~~~~~~~~~~
Extra zesty disclaimer:  MINE! MINE! ALL MINE! <chortle snort froth drool>
Robert K. "Zeke" Scott        internet: zeke at eta.cdc.com
Control Data Corp, Supercomputer Support Group