howto/ganeti: deleting an iSCSI LUN on gnt-chi

howto/ganeti.md

@@ -680,6 +680,28 @@ machine, see [resizing under LVM](#resizing-under-lvm), [resizing without LVM, n
 partitions](#resizing-without-lvm-no-partitions), or [Resizing without LVM, with partitions](#resizing-without-lvm-with-partitions),
 depending on the situation.
 
+### Removing an iSCSI LUN
+
+Use this procedure before to a virtual disk from one of the iSCSI SANs.
+
+First, remove the multipath config and reload:
+
+    gnt-cluster command rm /etc/multipath/conf.d/test-01.conf
+    gnt-cluster command "multipath -r ; multipath -w <disk-wwid> ; multipath -r"
+
+Then, remove the iSCSI device nodes. Running `iscsiadm --rescan` does not remove
+LUNs which have been deleted from the SAN.
+
+Be very careful with this command, it will delete device nodes without prejudice
+and cause data corruption if they are still in use!
+
+    gnt-cluster command "find /dev/disk/by-path/ -name \*<san-wwid>-lun-<lun> -exec readlink {} \; | cut -d/ -f3 | while read -d $'\n' n; do echo 1 > /sys/block/\$n/device/delete; done"
+
+Finally, the disk group can be deleted from the SAN (all the virtual disks it
+contains will be deleted):
+
+    SMcli -n chi-san-03 -p $SAN_PASSWORD -S -quick -c "delete diskGroup [<disk-group-number>];"
+
 ### Adding disks
 
 A disk can be added to an instance with the `modify` command as