iSCSI lun resize

Igor, the trick is to partition the iSCSI device. I have not done this with iSCSI but have with a Fibre Channel SAN.

You made sdb a PV. LVM cannot resize a PV.
If you partitioned sdb and made sdb1 a PV then you could using iSCSI resize sdb, then make a new partition from the new free space on sdb... lets call this sdb5 (logical partition). Then pvcreate /dev/sdb5 then vgextend your VG onto /dev/sdb5 then resize the LV then grow the filesystem.

The problem may be that you need to reboot to get the kernel to re-read the partition table...

Alternativly present a new iSCSI LUN lets call this sdc. Make a PV on that and add that PV to the VG... then resize the LV then grow the filesystem.

Regards
Alex Owen