• Most HBA vendor-supplied drivers support only load-leveling
– Larger number of buffers can benefit:
• Systems with heavily loaded system buses • Long server-to-target links with no switch in between • Can prevent congestion from backing up into the fabric
System bus blocked
A C B
Other hosts affected
Traffic flow
Congestion backs up into fabric
Switch
Performance issues:
Most HBA vendors offer multipathing drivers, but most of them allow only load- leveling (manual assignment of LUNs to each data path), not true load- balancing (dynamic assignment of routes).
Systems with heavily loaded or overloaded system buses can also benefit from HBAs with large data buffers (aka a large number of buffer credits).
If congestion occurs on the system bus, buffers can hold the data until the system bus becomes available, allowing the fabric to continue delivering data to the HBA. If the fabric must stop delivering data because the host runs out of buffers, congestion can back up into the fabric, potentially affecting other hosts. Without a large data buffer, a heavily loaded system bus could force the Fibre Channel link to stop delivering data until the congestion clears.