Data Backup and Recovery

Estimating snapmirror bandwidth requirements given Oracle Log Change Data



     I was asked to calculate snapmirror transfer requirements for a customer, but all I have to go on is that they're oracle log change rate is between 0.5 MBps to 2 MBps and that they have an RPO of 24 hours.

Calculating the snapmirror requirements for the log changes is straightforward engouth, but I also need to factor in the amount of change in the database files too so I can use regularly replicated SMO recovery points to create a known good point into which the customer can replay the logs after a disaster.

What I'm not sure about is what kind of factor should I allow for database changes as a ratio to log file changes

i.e. if there is 100MB of log entrie and  there will be 120MB of changes to the database files  then the ratio wil be 1 : 1.2

I'd appreciate your thoughts on this.and any "rules of thumb" that you can share.





I do not think there can be one-size-fits-them-all answer. Oracle writes only intended changes in redo logs, but on storage level you have changed blocks. So if client changes 10 bytes you have at least 4K changed on NetApp. So you need to know at least database block size and application pattern. And then adjust for changes in the same block etc.

When I had to estimate SnapMirror bandwidth requirements, I simply set up snapshot schedule and computed delta between consequitive snapshots. You do not need more than two snapshots at any time so it is pretty much harmless w.r.t. to reserved space.