IBM i Disk should not be on the same adapter as tape or optical

There are several reasons why its not recommended to mix Disk with Tape or Optical on the same adapter, regardless of physical or virtual. Here are some of the reasons:

- Performance:  A big disadvantage is performance. An even bigger disadvantage is performance again which is explained here.
Sharing throughput could hinder the performance potential during backup/restore operations.
If disk are on the same adapter (versus separate adapters guaranteed by basic user or iASP on separate adapters), then you'd be reading from disks on the same adapter when saving or writing from disks on the same adapter while restoring.

- Maintenance:  If there is an issue with an adapter that needs replacement or power cycling, then you are out a disk path as well as a tape or optical device. If there is an issue with the adapter, then a backup cannot be performed before changing the adapter.

- Troubleshooting/Recovery: Many times there can be issues that require a reset of the adapter. This can be automatic (such as disk connection issues) or manual (such as QTAPARB holding a lock on the tape device). An adapter hosting disk units is not allowed to be manually IPLed, leaving your tape device unusable unit there is a full system IPL.

- Flexibility: If a tape device resides on an adapter that also hosts disk units, then that adapter cannot be logically moved to another partition.

- Potential lack of proper redundancy:  You'll be giving up a quarter to half of the ports on the card which may reduce redundancy protection. It may not, depending on your configuration. Ideally there would be different adapters, different ports, different VIO Servers (if hosted), different switches, and different external storage ports. Giving up a port may create a single point of failure or leave a single point of failure vulnerable if its redundant path goes down.

- Expandability: If a tape or optical is using up the port, then this may limit or prevent easily adding more disk units. Current limits allow up to 127 active paths per port. Additional active paths will require additional ports or virtual adapters.