Once in a while it's required to resize iSCSI volumes to provide more space. Question is, how does one resize it without shutting down services? How does one do it when there's an extra layer called XenServer to worry about? The following will show you exactly how to do this. Also, this can easily be used on LVM over iSCSI without XenServe as well, pretty much the same procedure except the last step is not necessary.
1. Expand iSCSI volume using your SAN management tool.
2. Rescan iSCSI and reload multipathd on all nodes:
iscsiadm -m node -R; /etc/init.d/multipathd reload
3. Find out SCSI ID from XenCenter or xe command (multipath -ll will also provide this info). Use the SCSI ID in the following command (on a single node only):
pvresize /dev/mapper/<SCSI ID>
4. Verify that the size is now correct:
pvdisplay /dev/mapper/<SCSI ID>
5. Last command. We need to get XenServer to recognize the new size:
xe sr-update uuid=<SR UUID>
6. Now verify in XenServer that the size is correct. Now go grab a drink. Yes, that's part of the procedure.