Disk add to existing volume group proceeding very slowly

I have a volume group on an E26xx that has five 10TB volumes in it. I needed to add additional drives to the volume group and create another volume. I find that I can only select up to 2 drives for addition and after the addition, the process is taking a long time to complete. It's been running almost 5 hours ands is only 8% complete. Is this a normal pace for the E2600 when adding drives to a volume group? The drives are all 4TB 7200rpm disks.