Device Mapper Multipath Enablement Kit for HP StorageWorks Disk Arrays v4.2.1 release notes (AA-RWF9H-TE, March 2009)

Overview
This release notes discusses the recent product information about HP Device Mapper Multipath (HPDM
Multipath) Enablement Kit for HP StorageWorks Disk Arrays v4.2.1. This incremental release is to
support SUSE Linux Enterprise Server 11 operating system.
Device Mapper Multipath offers the following features:
• I/O failover and failback: Provides transparent failover and failback of I/Os by rerouting I/Os
automatically to an alternative path when a path failure is sensed and routing them back when
the path is restored.
• Path grouping policies: Paths are coalesced based on the following path-grouping policies:
1. Priority based path-grouping
• Provides priority to group paths based on Asymmetric Logical Unit Access (ALUA) state
• Provides static load balancing policy by assigning user defined priority to the path
2. Multibus
• All paths are grouped under a single path group
3. Group by serial
• Paths are grouped together based on controller serial number
4. Failover only
• Provides failover without load balancing by grouping the paths into individual path groups
• I/O load balancing policies: Provides the following load balancing policies within a path group:
1. Weighted Round Robin
This round-robin algorithm routes rr_min_io number of I/Os on a selected path before
switching to the next path.
2. Least pending I/O path
This determines the number of non-serviced requests pending on a path and selects the path
which has the least number of pending requests for service.
3. DM service time
This is a service time oriented dynamic load balancer, which selects a path to complete the
incoming I/O with the shortest time.
• Device name persistence: Device names are persistent across reboots and Storage Area Network
(SAN) reconfigurations. Device Mapper also provides configurable device name aliasing feature
for easier management.
• Persistent device settings: All the device settings such as load balancing policies, path grouping
policies are persistent across reboots and SAN reconfigurations.
• Device exclusion: Provides device exclusion feature through blacklisting of devices.
• Path monitoring: Periodically monitors each path for status and enables faster failover and failback.
• Online device addition and deletion: Devices can be added to or deleted from Device Mapper
(DM) multipath without rebooting the server or disrupting other devices or applications.
• Management Utility: Provides Command Line Interface (CLI) to manage multipath devices.
• Boot from SAN: Provides multipathing for operating system installation partitions on SAN device.
Device Mapper Multipath Enablement Kit for HP StorageWorks Disk Arrays v4.2.1 release notes 3