Weeehaaa! I got it!
But first replies to your questions:
RAID can handle this array
Linux jupiter.niersc.spb.ru 18.104.22.168-42.fc8 #1 SMP Tue Oct 30 13:18:33 EDT 2007 x86_64 x86_64 x86_64 GNU/Linux
bash: fdisk: command not found
cat: /proc/mdadm: No such file or directory
We installed another drive (on IDE bus) with 180GB and installed linux (also fedora 8) on it. After that we had four devices
/dev/cda1 - /boot partition on small IDE HDD (actually ~10 MB)
/dev/cda2 - / partition on small IDE HDD (actually ~160 GB)
/dev/cdb1 - /boot partition on RAID (actually ~10 MB)
/dev/cdb2 - / partition on RAID (actually ~3.4 TB)
and with this configuration also only 1.4T was accessible at /dev/cdb2
Only after we removed the boot partition /dev/cdb1 we managed to allocate all 3.4 TB on this device.
After that I created another volume group, and created a volume based only on /dev/cdb/ and created logical volume of 3TB without a probelm!
Similar problem is known in MS Windows. The disk which contains the MBR (master boot record, located on the 0 track, equal to the linux /boot) cannot be used to more than ~2TB. If the disk doesnt contain MBR it can be used to full extent.
Thank you guys for your interest and for your prompt replies/questions!