LUSE best practices

[Greynolds]

Is it best, performance wise that is, to create the luse within the PG or would one select ldevs from different PG's

Thanx in advance

[EDR]

Hi Greynolds,

Best practice would be to select devices from different PG's. Also, try to keep the number of devices in your LUSE low, since creating a LUSE is only a concatination of devices. The following, is a doc that I keep around that best describes the "performance considerations" when choosing to create a LUSE. I hope this helps...

LUSE Queuing Affects

Performance is a complex interrelationship of a number of factors that are related to the application. When the controller is first installed, the application may be able to get acceptable performance with LUSE. This can help to create a performance legend. As the Server's workload grows, the server may not be able to fully exploit the hardware capacity of the HDS controller. The software and hardware queuing affect of a LUSE serves as a limiting factor to the server ability to process transactions. This limitation can take place before the LUNS in the LUSE reach maximum usage.

For illustration purposes all the details are left out to focus on the predominant affect of the queuing phenomena.

If HOST1 has 5 LUNS in a LUN configured as LUSE, the host will maintain one IO Queue for the LUSE. If HOST2 has 5 LUNS configured as 5 separate LUNS, the host will maintain 5 IO Queues. HOST1 will initiate IO's from 1 Queue for the LUSE to the limit of IO's for a LUN at one time. HOST2 will initiate IO's from 5 Queues to the limit of 5 times the limit of IO's for a LUN at one time. The parallelism is significantly increased by the use of the 5 LUNS instead of 1 LUSE.