Levels 46–49: Storage Networking & SAN

Level 46: iSCSI Initiators & Targets

SCSI storage commands over an ordinary IP network. The initiator asks, the target offers.

Command	What it does
`iscsiadm -m discovery -t sendtargets -p 192.168.1.20`	Discover targets on a portal
`iscsiadm -m node -T <iqn> -p <portal> --login`	Log into a target, establish the session
`iscsiadm -m session`	List active sessions
`iscsiadm -m node -T <iqn> --logout`	Cleanly disconnect
`targetcli`	Configure an iSCSI target (server side)

Manually mounting shares doesn’t scale past a handful of machines. autofs mounts on access, unmounts after a timeout.

Command	What it does
`systemctl status autofs`	Check the autofs service
`systemctl reload autofs`	Apply new map entries without a full restart
`cat /etc/auto.master`	Show the top-level autofs map
`mount`	See everything currently mounted
`umount -f /mnt/nfs`	Force-unmount a stale/unreachable share

A server connected to storage over multiple redundant paths, made to look like one reliable device.

Command	What it does
`multipath -ll`	List multipath devices and path states
`ls -la /dev/disk/by-id/`	Identify devices by WWN, not changeable /dev names
`systemctl restart multipathd`	Restart the multipath daemon
`multipath -f mpatha`	Flush one named device map

FC is the older, dedicated-fabric sibling of iSCSI. Different tools, same troubleshooting instinct.

Command	What it does
`lsscsi`	List every SCSI device (iSCSI and FC alike)
`echo "- - -" \| tee /sys/class/scsi_host/host0/scan`	Rescan a host for new LUNs
`cat /sys/class/fc_host/host0/port_state`	Check an FC HBA port’s link state
`multipath -F`	Clean up every unused multipath map at once