Steps to extend a SAN disk under Linux multipath

Suppose you are using a 250 GB SAN disk under multiapth. You need to extend it to 500G. You need to extend LUN on storage side and follow below steps on Linux to extend LUN on multiapth level.

 # multipath -ll mpath111

mpath111 (01234567890123456789) dm-122 MSA2012i

[size=250G][features=1 queue_if_no_path][hwhandler=0][rw]

\_ round-robin 0 [prio=0][active]

 \_ 8:0:0:99  sdab       88:888   [active][undef]

 \_ 9:0:0:99  sdbm       77:777     [active][undef]

>>Resacan all paths of disk

# echo 1 >/sys/block/sdab/device/rescan

# echo 1 >/sys/block/sdbm/device/rescan

>> Confirm new size one each path

# fdisk -l /dev/sdab

# fdisk -l /dev/sdbm

>> Reread device map  and create/extend partition

# kpartx -a -v /dev/mapper/mpath111

# multiapth -v2 mpath111 OR service multipathd restart

# fdisk -l /dev/mapper/mpath111 (delete partition and create again WITHOUT existing fdisk !)

# kpartx -a -v /dev/mapper/mpath111

# dmsetup info /dev/mapper/mpath111 |gerp Status (should be Active)

# multipath -ll mpath111

mpath111 (01234567890123456789) dm-122 MSA2012i

[size=500G][features=1 queue_if_no_path][hwhandler=0][rw]

\_ round-robin 0 [prio=0][active]

 \_ 8:0:0:99  sdab       88:888   [active][undef]

 \_ 9:0:0:99  sdbm       77:777     [active][undef]

Notes

1- Run kpartx with -a -p p -v  option on rhel >= 62

2- If kpartx fails with  'device-mapper: resume ioctl failed: Invalid argument', upgrade device-mapper-multipath >=0.4.7-59
3- Multiapthd can be restart even when paths are are online and use.