IBM DS8000 manual Multipath I/O Mpio, Example A-7 lsvpcfg command

Path#	Adapter/Hard Disk	State	Mode	Select	Errors
0	fscsi2/hdisk17	OPEN	NORMAL	0	0
1	fscsi2/hdisk19	OPEN	NORMAL	27134	0
2	fscsi3/hdisk21	OPEN	NORMAL	0	0
3	fscsi3/hdisk23	OPEN	NORMAL	27352	0
DEV#:	1 DEVICE NAME: vpath4	TYPE: 2107 POLICY:		Optimized

SERIAL: 20522873

==========================================================================

Path#	Adapter/Hard Disk	State	Mode	Select	Errors
0	fscsi2/hdisk18	CLOSE	NORMAL	25734	0
1	fscsi2/hdisk20	CLOSE	NORMAL	0	0
2	fscsi3/hdisk22	CLOSE	NORMAL	25500	0
3	fscsi3/hdisk24	CLOSE	NORMAL	0	0

This lsvpcfg command helps verify the vpath configuration state. See Example A-7.

Example: A-7 lsvpcfg command

vpath0 (Available pv) 018FA067 = hdisk1 (Available) hdisk3 (Available) hdisk5 (Available) vpath1 (Available ) 019FA067 = hdisk2 (Available) hdisk4 (Available) hdisk6 (Available)

The hd2vp command converts a volume group made of hdisk devices to an SDD vpath device volume group. Run hd2vp <volumegroup name> for each volume group to convert.

Multipath I/O (MPIO)

AIX MPIO is an enhancement to the base OS environment that provides native support for multi-path Fibre Channel storage attachment. MPIO automatically discovers, configures, and makes available every storage device path. The storage device paths are managed to provide high availability and load balancing of storage I/O. MPIO is part of the base kernel and is available for AIX 5.2 and AIX 5.3.

The base functionality of MPIO is limited. It provides an interface for vendor-specific Path Control Modules (PCMs) which allow for implementation of advanced algorithms.

IBM provides a PCM for DS8000 that enhances MPIO with all the features of the original SDD. It is called SDDPCM and is available from the SDD download site (refer to 15.2, “Subsystem Device Driver” on page 324)

There are some reasons to prefer MPIO (with SDDPCM) to traditional SDD:

￿Performance improvements due to direct integration with AIX

￿Better integration if different storage systems are attached

￿Easier administration through native AIX commands

Important: If you choose to use MPIO with SDDPCM instead of SDD, you have to remove the regular DS8000 Host Attachment Script and install the MPIO version of it. This script identifies the DS8000 volumes to the operating system as MPIO manageable. Of course, you can’t have SDD and MPIO with SDDPCM on a given server at the same time.

Note: At initial GA, there will be no AIX MPIO support for the DS8000.

For basic information about MPIO see the “Multiple Path I/O” section in the AIX 5L System Management Concepts: Operating System and Devices guide:

350DS8000 Series: Concepts and Architecture