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324 DS8000 Series: Concepts and Architecture
Novell Netware
VMware 2.5.0
SuSE SLES9
15.2 Subsystem Device Driver
To ensure maximum availability most customers choose to connect their open systems hosts
through more than one Fibre Channel path to their storage systems. With an intelligent SAN
layout this protects you from failures of FC HBAs, SAN components, and host ports in the
storage subsystem.
Some operating systems, however, can’t deal natively with multiple paths to a single disk;
they see the same disk multiple times. This puts the data integrity at risk, because multiple
write requests can be issued to the same data and nothing takes care of the correct order of
writes.
To utilize the redundancy and increased I/O bandwidth you get with multiple paths, you need
an additional layer in the operating system’s disk subsystem to recombine the multiple disks
seen by the HBAs into one logical disk. This layer manages path failover, should a path
become unusable, and balancing of I/O requests across the available paths.
For most operating systems that are supported for DS8000 attachment, IBM makes the IBM
Subsystem Device Driver (SDD) available at no additional charge, to provide the following
functionality:
Enhanced data availability through automatic path failover and failback
Increased performance through dynamic I/O load-balancing across multiple paths
Ability for concurrent download of licensed internal code
User configurable path-selection policies for the host system
SDD can be downloaded from:
http://www.ibm.com/servers/storage/support/software/sdd/downloading.html
When you click the Subsystem Device Driver downloads link, you will be presented a list of
all operating systems for which SDD is available. Selecting one leads you to the download
packages, the
SDD User’s Guide, SC30-4096, and additional support information. The user’s
guide contains all the information that is needed to install, configure, and use SDD for all
supported operating systems.
For some operating systems, additional information about SDD can be found in Appendix A,
“Open systems operating systems specifics” on page 343.
IBM AIX alternatively offers MPIO, a native multipathing solution. It allows the use of
Path
Control Modules
(PCMs) for optimal storage system integration. IBM provides SDDPCM, a
PCM with the SDD full functionality. See “IBM AIX” on page 347, for more detail.
IBM OS/400 V5R3 doesn't use SDD. It provides native multipath support since V5R3. For
details refer to Appendix B, “Using DS8000 with iSeries” on page 373.
Note: SDD and RDAC, the multipathing solution for the IBM TotalStorage DS4000 series,
can coexist on most operating systems, as long as they manage separate HBA pairs. Refer
to the documentation of your DS4000 series storage system for detailed information.