Multipathing On Unix

Storage arrays:

Active-active: A LUN to be presented on more than one controller, normally two.

Active-passive: A LUN is only presented on one controller.

Veritas DMP: Sits above Unix SCSI driver layer. It uses SCSI inquiry command to determine multiple paths to a storage device/disk. The command is '/etc/vx/diag.d/vxdmpinq /dev/vx/rdmp/Disk_0s2'. Vertias metanodes/metadevices are created in /etc/vx directory. vxdmpadm or vxdisk path shows information about VxVM metadevices. Veritas uses 'Disk access name' or 'Disk media name' to identify disks. DMP has a modular architecture. Array specific libraries (ASL) may be required as well as array policy modules (APMs)

Device discover commands in Unix:
Solaris: devfsadm (subsystem scan, updates device tree and loads device drivers)
AIX: cfgmgr (same as solaris command)
HPUX: ioscan followed by insf -e updates device tree and loads drivers
Linux: makedev only updates device tree. Scan and drive loading is mostly done at boot time
Veritas: vxdctl enable or vxdisk scandisks use vxconfigd to re-scan storage config and update in-memory data structures to reflect changes.