Permission denied exporting whole device

[g <sendmailtogoran@gmail.com>]

Hi all,

I want to export /dev/sdb. My /etc/nbd.conf is	

[generic]
    user = nbd
    group = nbd
[arch]
    exportname = /dev/sdb
    copyonwrite = true

On the client I invoke

nbd-client 172.16.0.2 -N arch /dev/nbd0

The server responds with

journalctl -u nbd.service -f

follwing

Jan 01 13:41:24 route nbd_server[851]: Spawned a child process
Jan 01 13:41:24 route nbd_server[859]: virtstyle ipliteral
Jan 01 13:41:24 route nbd_server[859]: connect from 172.16.0.1, assigned file is
/dev/sdb
Jan 01 13:41:24 route nbd_server[859]: No authorization file, granting access.
Jan 01 13:41:24 route nbd_server[859]: Could not open exported file /dev/sdb:
Permission denied
Jan 01 13:41:24 route nbd_server[859]: Exiting.
Jan 01 13:41:24 route nbd_server[859]: Connection dropped: Permission denied
Jan 01 13:41:24 route nbd_server[859]: Exiting.
Jan 01 13:41:24 route nbd_server[851]: Child exited with 1

How can I pass sdb to nbd-server without running it as root? What looks like a
good and safe way? I've tried it with sdb1 too (my preffered choice). Same
result.

Regards

Goran