Re: RMAN Backup Sets

Well, it's not just that. You've also got the size of the backup sets to consider and the effect of keeping a fast tape drive streaming on the rest of your system if you are doing hot-backups whilst users are still accessing the system. Likewise you might want to look at any OS restrictions that making large backup sets might impose. The capacity of your tapes drives, whether you are cutting off to disk first, etc. are all factors here.

I suppose once you've factored all the above in, you might want to perform some timed testing to see what effect filesperset has on your system. I can tell you that on our fast UNIX servers with DLT drives on their own dedicated FW SCSI controllers with the Oracle db on striped raw disks, even 1 fileperset keeps the tape drive running flat out at 8.5MB/s. Then again, if you pull multiple tablespaces into a backup set you could argue that with spread of I/O might keep your tape device streaming without straining the disk drives too much, it really does depend on your system. Of course if the strain was too much on your system when you did have the tape drive running flat out you could look at using the 'set limit' command.

Like I say, have a good think and do some testing. And you might want to rethink things if you switch to using multiple tape drives in parallel.

Steve Phelan

(Oralce 7 & 8 OCP)

frederick.r.hillebrandt_at_monsanto.com wrote:

> We are implementing RMAN for backup/recovery of our OLTP Oracle 8 instances.
> Can anyone tell me if they have an optimal method for determining number of
> files per backup set? I believe the objective is to keep the tape devices
> streaming.
>
> Fred Hillebrandt
> Monsanto IT - DBA Team
>
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Received on Thu Feb 25 1999 - 15:48:10 CST