The reason to turn off 3590E hardware compression, is if you having problems "feeding the beast". You get faster backups if you can keep the drive going.
An IBM 3590E writes to tape at 14 MBs. If hardware compression is turned on and you are getting 3:1 compression, then you have to feed the controller at 3*14 or 42 MBs. If you can, you have the best of both worlds, speed and amount of data on a single tape. If you can't then you need to choose speed vs high data storage. Doing software compression, only makes sense to me if you are going over slow (escon) channels. Given all that.... In DR tests, less tapes seems to be a good thing. The DR site has better, faster, hardware then most of our shops. (everything is ficon) You may buy less MIPS but you can't buy less I/O thruput. It takes more CPU to compress data then it takes to expand the data. i.e. worry about your own MIPS. In general, I don't see the benefit in software compression, when hardware compression is available. But if you tested the difference in your site, and you have come to a software compression conclusion, more power to you. Each site has a different set of concerns. Tom Duerbusch THD Consulting >>> Alain Benveniste <a.benveni...@free.fr> 4/30/2009 6:25 AM >>> Richard, You have the same questions I had when I started to put in place our DR solution. We also have 3590E drives and I never tried to remove the hard drive default compaction. I don¹t see a reason for that. Now choosing software compaction is a must if you have enough cpu to do the work for backup and ALSO for restore. For us we can spend more time to use software compaction because we know that we have enough cpu to do the work at restore time offsite. The gain at restore justifies to take more time at backup processing. It¹s true too that software compaction takes less tapes than with no compaction. If you have many dasds to backup and a time constraint to restore i would suggest you to both use hard and software compactions. Our idea is to say that when we restore in a DR test the cpu is used ONLY for restore. Why not fully using it ! Regards Alain Benveniste Le 29/04/09 20:46, « Schuh, Richard » <rsc...@visa.com> a écrit : > We are working on a DR process. I notice that the defaults for a Hidro backup > include the PACK option which tells Hidro to pack, or condense in some > fashion, its output. The output is being written to 3590E drives. It appears > that there are three choices we can make for condensing the data: software > only, hardware only, or a combination of the two (uncompacted was purposely > omitted from the list). Which is likely to give the best results? Does > software compaction produce consistently lower output volumes than letting the > drive do it? Is there anything to be gained by using both h/w and s/w? > Obviously, software compaction costs in terms of cpu time. The question is, is > it worth the time spent? > > Regards, > Richard Schuh > > > >
