pg_basebackup running slow

Hello,

We are using postgresql 9.2 on redhat linux instance over openstack cloud.

Database is around 441 GB.

We are using below command to take backup:

pg_basebackup -v -D /pgbackup/$bkupdir -Ft -z -c fast

Backup size created is around 84GB.

However, it is taking almost 10 hr 21 minutes to complete.

Looking for speed improvement?

Thanks& Regards,

Vaze Swapnil