Storage Server IO
Storage unit Concurrent Jobs value and the disk pool Max IO Streams per volume value:
The Max IO Streams value for the disk pool sets the number of read/write operations that can run at the same time on the disk pool. The Concurrent Jobs value on the storage unit sets the maximum backup/restore jobs that can run at the same time to the storage unit. More than one storage unit can point to the same disk pool.
It is important that the total number of Concurrent Jobs from storage units that point to the same disk pool must not exceed the configured Max IO Streams value for the disk pool. So that secondary operations can perform, the total number of Concurrent Jobs set in the storage units that point to the same disk pool should not be higher than 90% of the total of the Max IO Streams value of the disk pool. This 10% allows the possibility of secondary operations running while backup/restore operations are maximized. Setting REPLICATION_TARGET_JOB_LIMIT to set limits on the number of A.I.R. Replication per target storage server helps to maximize the performance of each secondary operation. SLP parameters can be used to limit the number of secondary operations.
In summary, a disk pool is configured by default to have an unlimited value for Max IO Streams. It is recommended that the Max IO Streams for the pool be limited to a level that maximizes the number of jobs that can run, but is not too high that the disk pool performance is depreciated due to too many read/write operations occurring at the same time.
A storage unit that is configured to point to the disk pool should have a Concurrent Jobs value lower than the Max IO Streams value for the disk pool. The storage unit's Concurrent Jobs value will address backup jobs and restore jobs, but does not impact the number of secondary operations like duplications, replications, import type jobs. These secondary operations are managed by the SLPs and try to run as many as possible, usually dictated by the Max IO Streams count.
More information about configuring disk pools is also available:
See Best practices: Disk pool configuration - setting concurrent jobs and maximum I/O streams.