Once the initial backup has completed, backup performance is almost always limited by the client's disk I/O performance. Which back-end is used (Avamar vs. DataDomain) is largely irrelevant unless the Avamar grid is very small (1x3 or single node).
Assume a backup rate of about 100GB/hour for a standard Exchange client. For faster clients, disk benchmarking or a "degenerate" test can give you a ballpark figure of expected performance but be sure to build in a margin of safety.
It is critical that the disks on the Exchange client not be placed into contention (backing up multiple databases that reside on the same LUN will place that LUN in contention, for example) because contention drastically reduces the performance of the backup.
For extremely high performance Exchange systems (SAN-backed with independent RAID groups per database, for example), the standalone Avamar client is currently a better choice because DataDomain integration only supports a single backup stream in version 6.0.
In 6.1 multistreaming is available to DDOM correct? I have a 4tb Exchange system that I am going to be trying to roll in, is this a feasible scenario?
We are using this as of now we are backing up 2 tb dB in almost 3 hours with 4% new bytes so you can calliculate in according. we on avamar 6.0 with 6.0 client.