Assigning Device Names - HP StorageWorks MPX200 User Manual

NOTE:
The Linux driver supports both Red Hat 3 and SUSE 8. For information on how to configure the Linux
iSCSI initiator, see the Readme file in the tar ball.

Assigning device names

Linux assigns SCSI device nodes dynamically when it detects a SCSI logical unit; therefore, the
mapping from device nodes (such as /dev/sda and /dev/sdb) to iSCSI targets and logical units
may vary.
Variations in process scheduling and network delay can result in iSCSI targets being mapped to
different SCSI device nodes each time the driver is started. Therefore, configuring applications or
operating system utilities to use the standard SCSI device nodes to access iSCSI devices can result in
SCSI commands being sent to the wrong target or logical unit.
To ensure consistent naming, the iSCSI driver scans the system to determine the mapping from SCSI
device nodes to iSCSI targets. The iSCSI driver creates a tree of directories and symbolic links under
/dev/iscsi to facilitate access to a logical unit of an iSCSI target.
The directory tree under /dev/iscsi contains subdirectories for each iSCSI bus number, each target
ID number on the bus, and each LUN for each target. For example, the disk device for bus 0, target
ID 0, and LUN 0 would be /dev/iscsi/bus0/target0/LUN0/disk.
Each logical unit directory contains a symbolic link for each SCSI device node that can connect to
that logical unit. The symbolic links are named using the Linux devfs naming convention.
• The symbolic link disk maps to the whole-disk SCSI device node (for example, /dev/sda or /
dev/sdb).
• The symbolic links, part1 through part15, map to each partition of the SCSI disk. For example,
a symbolic link can map to partitions /dev/sda1 and dev/sda15, or to as many partitions as
necessary.
NOTE:
The symbolic links exist regardless of the number of disk partitions. Accessing a partition name
results in an error if the partition does not exist on the disk.
• The symbolic link mt maps to the auto-rewind SCSI tape device node for the LUN (for example,
/dev/st0). Additional links for mtl, mtm, and mta map to the other auto-rewind devices (for
example,/dev/st0l, /dev/st0m, /dev/st0a), regardless of whether those device nodes
exist or can be opened.
• The symbolic link mtn maps to the no-rewind SCSI tape device node, if any. (For example, this
LUN maps to /dev/nst0.) Additional links (formtln, mtmn, and mtan) map to the other no-
rewind devices (for example, /dev/nst0l, /dev/nst0m, /dev/nst0a), regardless of
whether those device nodes exist or can be opened.
• The symbolic link cd maps to the SCSI CD-ROM device node, if any, for the LUN (for example,
/dev/scd0).
• The symbolic link generic maps to the SCSI generic device node, if any, for the LUN (for example,
/dev/sg0).
80 MPX200 iSCSI configuration rules and guidelines