I have an Linkstation HD-H250LAN with firmware 2.30. There are no users or groups defined except the defaults. The Linkstation is a member of the same workgroup as a Vista machine and an XP machine. There is a 1.5 terabyte disk attached to the rear USB port. I backup the Vista machine to a folder on the USB disk called Backup Vista and I backup the XP machine to a folder called Backup XP. I am using robocopy to do the backups on each machine and each machine created its own backup folder on the USB attached disk. All of this works as planned until for some unknown reason the Backup XP folder becomes owned by root and cannot be accessed. I am viewing the security information from the Vista machine. The folder, when it is accessable, is owned by Everyone, nobody (HD-HLANE7B\nobody), nogroup (HD-HLANE7B\nogroup). When the folder is not accessable it is owned by root (HD-HLANE7B\root). The only option I seem to have is to delete the folder and let the XP machine recreate it. This effectively makes the backup useless. I have searched the board but didn't find any solutions.
Few things going on here that I want to clarify. Robocopy is unstable with nas device's along with windows xp. Firmware for this hd-h250lan is at 1.61. I don't know how you got firmware 2.30. But I don't believe that is from us. Also making sure that you format the usb hard drive to xfs to properly use it is important. And hooking up a 1.5 tb ext hd to a 250gig nas is a little extreme also. I need to verify this, but should work up to 1tb ext hd.
I've been successfully using robocopy for years. The Linkstation determines the disk format which is EXT3. The problem I am trying to solve is ownership of the folder and the fact that the Linkstation changes it. I have never loaded any firmware other than Buffalo and I can't remember upgrading the firmware but maybe I did a long time ago.
System Status
LinkStation Name
HD-HLANE7B
LinkStation Description 
LinkStation Firmware Version
2.30
DHCP Client
Disable
IP Address
192.168.1.150 (Manually Assigned)
Subnet Mask
255.255.255.0
MAC Address
withheld Microsoft
Workgroup
SILLY
FTP Server
Disable
NTP Function
Enable(2009/08/24 09:30:03 Renew)
Drive Capacity
239,722,336 kbytes
rive Space Used
167,514,572 kbytes
Percentage in Use
69.88 %
SB Disk1Drive Capacity
1,442,145,212 kbytes
USB Disk1Drive Space Used
193,131,624 kbytes
USB Disk1Percentage in Use
13.39 %
USB Disk1 Format Type
EXT3
Local Date and Time 
2009/08/24 10:16:40