HP 3PAR SUSE Linux Enterprise Implementation Guide

Target Port Limits and Specifications for iSCSI
To avoid overwhelming a target port and ensure continuous I/O operations, observe the following
limitations on a target port:
• I/O queue depth on each HP 3PAR StoreServ Storage HBA model, as follows:
QLogic 1G: 512◦
◦ QLogic 10G: 2048 (HP 3PAR StoreServ 10000 and HP 3PAR StoreServ 7000 systems
only)
• The I/O queues are shared among the connected host HBA ports on a first-come, first-served
basis.
• When all queues are in use and a host HBA port tries to initiate I/O, it receives a target queue
full response from the HP 3PAR StoreServ Storage port. This condition can result in erratic I/O
performance on each host. If this condition occurs, each host should be throttled so that it
cannot overrun the HP 3PAR StoreServ Storage port's queues when all hosts are delivering
their maximum number of I/O requests.
HP 3PAR Priority Optimization
The HP 3PAR Priority Optimization feature introduced in HP 3PAR OS versions 3.1.2. MU2 is a
more efficient and dynamic solution for managing server workloads and can be utilized as an
alternative to setting host I/O throttles. Using this feature, a storage administrator is able to share
storage resources more effectively by enforcing quality of service limits on the array. No special
settings are needed on the host side to obtain the benefit of priority optimization although certain
per target or per adapter throttle settings may need to be adjusted in rare cases. For complete
details about how to use HP 3PAR Priority Optimization (Quality of Service) on HP 3PAR StoreServ
Storage arrays, see the HP 3PAR Priority Optimization technical whitepaper, which is available
on the HP SC website:
HP 3PAR Priority Optimization
HP 3PAR OS Persistent Ports
The HP 3PAR OS Persistent Ports (or virtual ports) feature minimizes I/O disruption during an
HP 3PAR StoreServ Storage online upgrade or node-down event (online upgrade, node reboot,
or cable pull test). Port shutdown or reset events do not trigger this feature.
Each iSCSI target storage array port has a partner array port automatically assigned by the system.
Partner ports are assigned across array node pairs.
HP 3PAR OS Persistent Ports allows an HP 3PAR StoreServ Storage iSCSI port to assume the identity
(port IP address) of a failed port while retaining its own identity. Where a given physical port
assumes the identity of its partner port, the assumed port is designated as a persistent port. Array
port failover and failback with HP 3PAR OS Persistent Ports is transparent to most host-based
multipathing software, which can keep all of its I/O paths active.
NOTE: Use of HP 3PAR OS Persistent Ports technology does not negate the need for properly
installed, configured, and maintained host multi-pathing software.
For a more complete description of the HP 3PAR OS Persistent Ports feature, its operation, and a
complete list of required setup and connectivity guidelines, see:
• The HP Technical white paper HP 3PAR StoreServ Persistent Ports (HP document
#F4AA4-4545ENW)
This document is available on the following HP SC website:
Target Port Limits and Specifications for iSCSI 21