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Multipathing Using Adaptec Host Bus
Adapters
There are many similarities between the LSI and Adaptec SAS host bus adapters,
and much of the discussion in “Multipathing Using LSI Host Bus Adapters” on
page 54 is relevant to Adaptec controllers as well. There are, however, important
differences between the LSI and Adaptec functionality.
When you have an Adaptec REM and you plug in a disk blade with eight
dual-pathed disk drives, the REM recognizes the disk drives as eight disks with dual
paths, but it does not present any disk drives to the server blade BIOS or the OS until
volumes are created. Volume creation using the Adaptec REM utilities is required.
The volumes can be either one-disk drive volumes or multi-disk drive RAID
volumes. The Adaptec REM can create up to 24 volumes.
Note – In a situation of one SAS-NEM and single paths, the same volume creation
requirement applies.
When volumes are created, the Adaptec REM presents each volume to the server
blade BIOS and OS as one disk drive. The dual paths are hidden.
This means that OS software for multipathing cannot be used because it cannot see
the two paths. With the Adaptec REM, the OS will never be presented with a disk
drive that is not in a volume. Using the Adaptec RAID manager software, you can
determine that two paths exist, but the OS still cannot recognize more than one.
Multipathing at the OS Level
The Solaris, Red Hat Linux 5.x, Windows Server 2008, and VMware ESX 3.5.
operating systems all have utilities for managing dual paths at the OS level. This
section contains the following subsections:
■
“Hardware RAID Hides Dual Paths From the OS” on page 58
■
“Multipathing With RHEL 5.x Linux and LSI Host Bus Adapters” on page 58
■
“Multipathing With the Solaris OS and LSI Host Bus Adapters” on page 59
■
“Multipathing With Windows Server 2008 and LSI Host Bus Adapters” on
page 62
■
“Multipathing with VMware ESX 3.5 and LSI Host Bus Adapters” on page 65
Chapter 6
Multipathing and RAID
57