RE: RMAN duplex backup. how many channels?

Russel, I've never actually used the duplex functionality, but from what I've read on it, I would recommend you continue to use 2, or maybe even 4 channels. The benefit of filesperset > 1 is that you can multiplex several datafiles into one backup piece, which is seen as a single file/image by your media management software - so it is more consolidated, plus it allows Oracle to backup faster because it can read from multiple files simultaneously and write them all to the tape at the same time, thus keeping the tape streaming so it doesn't have to incur the expense of stopping, rewinding and restarting.  

You just have to set duplex=2, and then allocate as many channels as you want (2 or 4 recommended - you should test both to see what performs better for your system) - the one duplex setting will apply to all channels. Also, you have to have backup_tape_io_slaves=true in order to use duplex. (according to TFM)  

Regards,
Brandon  

-----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org]On Behalf Of rjsearle_at_gmail.com Sent: Friday, July 15, 2005 5:10 AM
To: Oracle-L (E-mail)
Subject: RMAN duplex backup. how many channels?

HI,  

We have finally restored and recovered from a near death experience with multiple disk crashes and tape failures. Our env is Solaris (SunOS5.8) and ORA 8.1.7.0.0  

The recovery was incomplete-cancelled and subsequently opened with resetlogs. So I'm thinking it might be backup time!  

I had no experience with rman b4 this episode. I am scouring manuals to determin the appropriate rman command to do a duplexed cold backup Our backups are normally hot using rman. we have 2 tape drives attached directly to the box and normally allocate 2 channels, 4 files per set as follows:  

run {
allocate channel t1 type 'SBT_TAPE' parms 'ENV=(NSR_DATA_VOLUME_POOL=GCLCDWP)';

allocate channel t2 type 'SBT_TAPE' parms 'ENV=(NSR_DATA_VOLUME_POOL=GCLCDWP)';  

backup database
filesperset 4
include current controlfile
archivelog all delete input
format 'FULL_DW_%d_%u';  

release channel t1;
release channel t2;
}
   

For this backup I want 2 copies so I have discovered 'set duplex = 2'. If I use this cmd in our env with only 2 drives, how many channels should I allocate? I can't find anything in TFM to clarify but then again I am now sleep deprived.  

Also, I am unclear of the benefit of setting filesperset to values >1. I'd love to hear your thoughts.  

Could the resident experts kindly review this run cmd and comment appropriately?  

reset database # this is required due to the resetlogs  

run {
set duplex = 2;

allocate channel t1 type 'SBT_TAPE' parms 'ENV=(NSR_DATA_VOLUME_POOL=GCLCDWP)';  

backup database
filesperset 1
include current controlfile
format 'FULL_DW_%d_RESETLOGS_%u';  

relese channel t1;
}
 

Thanks
Russell    

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