Help with install client command via command line from Windows. (HELP!!!)

Simplegifts,

This is to split the backup for our file print server, we have 12 drives. Because file print server has so many files, trying to split into 2 clients running on the same physical server so the scan wouldn't take as long. We have it running but I client to 18.1 from 7.4

Configurations with multiple concurrent avtar instances are not officially supported.  If you previously had Engineering approval for such a configuration (through an approved "RPQ") and the client has since been upgraded you would need to request an updated RPQ for the new configuration from your local DellEMC account team.

There are many possible ways to speed up backup performance and since multiple concurrent avtars isn't a supported feature, it's typically one of the last options that would be considered.  The following article walks you through how to understand and optimise Avamar backup performance with a view to minimising backup duration.

KB 335029 - Avamar client backup performance - how to identify bottlenecks (RESOLUTION PATH)

Configurations with multiple concurrent avtar instances are not officially supported

technically that's incorrect as that's how clustering does it, doing it for non clustered solutions might not be supported..... NOTE you can have a single node cluster if that helps get you those supported multi instances you need.....making the same effective result as you would get via RPQ except the services are added to the cluster instances not the server itself.

BUT I digress. you can always do it as an agent instigated backup instead.

each specifies its own set of cache files, etc and its thus multiple parallel backups to one instance can run at a time. The different cache files (set the cache prefix) are there so you can run more than one backup at a time.
NOTE : only one at a time via the scheduler per instance is a limit of the scheduler not the application itself and the multi instance RPQ is about adding instances to get around the scheduler limitation not a limitation in the number of parallel avtar processes allowed on any said host being backed up. 

The activity monitor wont show this as the scheduler knows nothing about it so you need another mechanism to monitor the backup completion.

and yes poor design of file servers can see you try and backup an insane amount sequentially. You really need to look at how this is being done and address as sequential disk backups will see the disk be the bottle neck every time. The larger the fileserver the more you notice this ie 20+TB with IOPS limits makes you want to punish those that didn't think about better ways to backup the server than sequentially.