HP EVA Array iSCSI Connectivity Option - Manual (Page 80)

NOTE:
These symbolic links exist regardless of the number of disk partitions. Opening the partition devices
results in an error if the partition does not actually exist on the disk.
• The symbolic link mt maps to the auto-rewind SCSI tape device node for the LUN /dev/st0, for
example. Additional links for mtl, mtm, and mta map to the other auto-rewind devices /dev/st0l,
/dev/st0m, /dev/st0a
, regardless of whether these device nodes actually exist or could 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 such as /dev/nst0l, /dev/nst0m, /dev/nst0a, regardless of whether those device
nodes actually exist or could be opened.
• The symbolic link cd maps to the SCSI CD-ROM device node, if any, for the LUN /dev/scd0
for example.
• The symbolic link generic maps to the SCSI generic device node, if any, for the LUN /dev/sg0.
Because the symlink creation process must open all of the SCSI device nodes in /dev in order to
determine which nodes map to iSCSI devices, you may see many modprobe messages logged to
syslog
indicating that modprobe could not find a driver for a particular combination of major and
minor numbers. This message can be ignored. The messages occur when Linux is unable to find a driver
to associate with a SCSI device node that the iSCSI daemon is opening as part of its symlink creation
process. To prevent these messages from occurring, remove the SCSI device nodes that do not contain
an associated high-level SCSI driver.
Target bindings
The iSCSI driver automatically maintains a bindings file, /var/iscsi/bindings. This file contains
persistent bindings to ensure that the same iSCSI bus and target ID number are used for every iSCSI
session with a particular iSCSI TargetName, even when the driver is repeatedly restarted.
This feature ensures that the SCSI number in the device symlinks (described in
“ Device names ” on page 79) always map to the same iSCSI target.
NOTE:
Because of the way Linux dynamically allocates SCSI device nodes as SCSI devices are found, the driver
does not and cannot ensure that any particular SCSI device node /dev/sda, for example, always maps
to the same iSCSI TargetName. The symlinks described in “ Device names ” on page 79 are
intended to provide application and fstab file persistent device mapping and must be used instead of
direct references to particular SCSI device nodes.
If the bindings file grows too large, lines for targets that no longer exist may be manually removed
by editing the file. Manual editing should not be needed, however, since the driver can maintain up
to 65,535 different bindings.
Mounting file systems
Because the Linux boot process normally mounts file systems listed in /etc/fstab before the network is
configured, adding mount entries in iSCSI devices to /etc/fstab will not work. The iscsi-mountall
script manages the checking and mounting of devices listed in the file /etc/fstab.iscsi, which has
the same format as /etc/fstab. This script is automatically invoked by the iSCSI startup script.
NOTE:
If iSCSI sessions are unable to log in immediately due to network or authentication problems, the
iscsi-mountall
script can time out and fail to mount the file systems.
80 Setting up the iSCSI Initiator and storage