Direct SQL Backup is very slow over the LAN

Hi,

Within LAN I have a Computer (A) where I have all my SQL Server Databases
and I have another Computer (B) where I want to take backup of these
databases. From B, I connect A and issue BACKUP DATABASE statement to write
backup file in B like this:

BACKUP DATABASE xxx TO DISK = '\\B\D\Backup\xxx.bak'

The Computer B has got upgraded recently to double the size of HDD. Earlier
it was with 250 X 6 RAID and now it is 500 X 6 RAID. A 25 GB database file
took the following time to backup:

(a) Backup within A - 18 min
(b) Backup from A to B before recent upgrade - 20 min
(c) Backup from A to B after recent upgrade - 2 Hours & 30 min
(d) Backup within B - 24 min

Both A and B have similar confuguration like Windows 2003 R2 O/S, 4 GB RAM,
3.6 GHz CPU, Network Card etc. However, a remote iSCSI device had been added
to B for some other backup purpose and I believe it has nothing to do with
this performance issue.

I do expect the time count similar/near to (b) above even after the upgrade.
What could have gone wrong during the upgrade? Can anyone help?

Regards,
Shekhar.