Ignite-UX and SAS white paper

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Introduction
The following white paper is intended to explain how to use SAS disks with Ignite-UX to allow you
to install and recover your systems without having to worry about Ignite-UX restrictions with SAS.
Agility and what Ignite-UX knows about SAS
SAS disks are identified to a system with a unique World-Wide Name (WWN) also known as a
SAS address.
The I/O stack on HP-UX 11i v2 internally associates that WWN to a hardware path. The hardware
path is not a typical hardware path since the hardware path can change if you reinstall or recover
the system and the SAS configuration has changed.
On HP-UX 11i v3, legacy device special files (DSFs) for SAS devices are handled similarly to 11i
v2. Therefore, if the SAS configuration changes, the legacy DSFs for SAS devices can change
during an installation or recovery session.
With persistent DSFs on 11i v3 there is reliable mapping between a SAS device and the persistent
DSF. Since the system knows about the correlation between the WWN and the persistent DSF
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Ignite-UX is able to keep the mapping between a persistent DSF and WWN when performing a
recovery. The information presented later in this white paper is not applicable to persistent DSFs, it
is aimed at HP-UX 11i v2 and legacy DSFs on HP-UX 11i v3.
Note:
You will have actions to perform when replacing a SAS device on HP-
UX 11i v3 since a persistent DSF is tied to a WWN. See the
io_redirect_dsf(1m) manual page on any HP-UX 11i v3 system for more
information. If you use legacy DSFs you may also need to use the
sasmgr(1m) command’s replace_tgt option.
Improvements Made in Recent Ignite-UX Versions
Ignite-UX continues to make improvements in managing SAS devices.
Release C.7.5 improved the identification of devices during recovery by saving WWN (or WWID)
information in the config files (in addition to the hardware path). This improvement allowed SAS
devices to be added, removed, or moved; and still be correctly chosen for installation during a
recovery. However, the hardware path and legacy device file names were different after a
recovery in this situation, resulting in the failure to import LVM data volumes due to the device file
names changing. Importing data volumes had to be done manually (the vgscan command could
be used in this case).
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Requires you to use Ignite-UX version C.7.2 or later to reliably recover persistent DSFs for SAS devices when you have more than 7 mass
storage devices connected to a system.