Overview: The Next Generation Mass Storage Stack (September 2009)

Agile View
The agile view includes a new persistent type of disk and tape DSF, and represents hardware pathing to disk
and tape devices in ways that support larger configurations and enable transparent multi-pathing.
The naming of DSFs and hardware paths is shown in Figure 2. Like the legacy view diagram, the HBAs are on the
left, disks are on the right, with connections in between them.
Following are important concepts displayed in Figure 2:
• The hardware path elements beyond the HBA are now printed in hexadecimal notation.
• The hardware paths follow a more natural addressing model: SCSI-2 for parallel SCSI and SCSI-3 for
Fibre Channel. Fibre Channel addressing is much longer than before, but is no longer forced into a SCSI-
2 paradigm. The address elements, such as the target port worldwide name, correlate directly to path
information displayed by the fcmsutil command and other disk array controller programs. If you
perform SAN configuration, these hardware paths are familiar to you.
• Each disk now has a virtualized hardware path known as the LUN hardware path, which represents
the disk itself–not the path to the disk. Despite having multiple hardware paths, the disk has only one LUN
hardware path. This hardware path starts with a virtual root address of 64000. Addressing beyond that
virtual root consists of a virtual bus address and a virtual LUN ID.
• The DSF name for each disk no longer contains path information. The multi-pathed disk has a single
persistent DSF regardless of the number of physical paths to it.
• The ioscan listing includes the following changes:
• The emulated domain, controller, target, and LUN for Fibre Channel have been removed. Entries in
the ioscan listing beneath the HBA for both parallel SCSI and Fibre Channel include a simplified
target path and lun path, shown as class tgtpath and lunpath, respectively.
• Each physical path to a disk is now referred to as a lunpath, and its hardware path is called a
lunpath hardware path. Multi-pathed disks have multiple lunpaths, and the description of the
lunpath refers to its assigned disk. Since the DSF refers to the disk rather than its path, lunpaths do not
have DSFs associated with them.
• Each disk has a single disk class entry. The hardware path shown by ioscan is the LUN hardware
path, the description is the same as the legacy view, and the DSFs are the persistent DSFs assigned to
the disk.
• Target paths now have a driver named estp. Lunpaths use the eslpt driver, and disks use a new
esdisk disk driver.
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