Factors affecting the NDMP backups

Hello,

In our environment, I come across situations where NDMP backup of some shares (with larger size) completes before the shares of smaller size.

I would like to know what are the factors which lead to long backup times for NDMP backups.

I do know that long backup durations are seen for shares containing millions of files. Are there any other parameters which will lead to increase in backup times or is this the only one?