Channel/device speeds If you are on ESCON, with 17 MB/s and going to an IBM 3590 tape drive, for example...
The B drives write to tape at 9 MB/s. The E/H drives write to tape at 14 MB/s. If you use tape controller hardware compression, say 3:1, you need to send at 3 times the data rate as the drive can write to the tape. i.e. the controller on a B drive, will have to receive data at a 27 MB/s, in order to be able to write to the tape at 9 MB/s. Not going to happen with ESCON. The E/H drives are even worse. You need FICON channels to handle these drives. And, you need FICON channels on the DASD to be able to read the data at these high rates. Otherwise, you shoe-shine the drives. Very time expensive. For my 3590B drives with 10 GB tapes, it takes about 75 minutes to fill the tape with tape controller compression turned on over ESCON channels. So, what kind of drives do you have and what kind of channels are they attached to (both disk and tape)? Tom Duerbusch THD Consulting >>> Alain Benveniste <[EMAIL PROTECTED]> 11/26/2008 11:35 AM >>> We are several guys to misunderstand something about compression. Here is the situation: Our interrogations come from MVS but I think it is true fo VM too. We did 2 backups with DFDSS, 1 with the COMPRESS option and 1 without. For the 1st one, the restore too 3h20, the 2nd 6hrs ! 25 output tapes for both tests. This was made on 2084 with 10 procs,and really enough mips. Ok the software compression is very cpu consumming, hardware no. The question is what a software compression does, IDRC doesn't. Several of us think the algorithm used is very similar from one to the other, so !. Why that difference ! Others think, that IDRC is off, even if it is coded in the system (I verified this twice). Others says, we didn't pay to use IDRC. Others remember we had to install IDRC in the old past. So we don't have it. I'm looking for a firefly in this dark mess. Alain Benveniste
