If you need to resize a iSCSI volume you need to:
I’ll skip the resize procedure on the target, because it depends on how it’s made (lvresize, dd, etc).
The procedure to rescan the volume on the initiator (open-iscsi) is very simple and can be accomplished online.
iscsiadm -m node -R
Then, you can grow the filesystem, if any (xfs_grofs, resize_reiserfs, resize2fs, depending on your fs type).