i have an external Buffalo RAID box fitted with 2 3TB WD Red drives. Using the box's XP mode the drive is in 2 partitions - 2199GB and 801GB (as shown in WD Data LifeGuard Diag). My question is - should the external box develop a fault e.g. power supply, would i still be able to access the data on the drives by plugging them in internally in the PC's SATA ports? I tried a new 3TB and XP didn't even see the drive. It didn't even show in Control Panel Disk Management.. One solution i am thinking of is to replace the 3TB drives with 2TB drives and use the 3TB drives in a NAS box that i will purchase at a later date. moving the data off the drive would be a nightmare though..

Your explanation is incomplete:

As I understand it, the external WD Buffalo is still working properly (?)
with internally 2x 3TB it shows in XP 2 partitions about 1x 800GB + 1x 2200GB

It looks like this unit is set up as Raid 1, where one of the internal drives is a 1.1
clone - i.e. both drives have similar content.

1) If its valuable data - organise a second external drive and copy all data on to it.
2) avoid any type of encryption on the new external system
3) Faulty power supply:
If you are lucky - and there is no active encryption set - both drives might still work
directly connected to a PC SATA port (remember - they have both the same content)
The power suppy is a weak point in such external systems - if the power supply is shot
- it might even have also shot BOTH harddisks (PCB or even more).
4) A NAS works internally with its own operating system (Linux) - to work with the 2x 3TB
out of the Buffalo system, you would need to copy the data off of it first, then check the
data, and if you are 1000% sure, that all is ok, install them into the NAS and then you
need to set it up - usually with the web browser to acces its firmware/software or with
its own installation software from CD/DVD.

Bear in mind a NAS (LAN) is slow, really slow - and then transferring huge data takes
"centuries" ...

In any DR case which might arise - I recommend to contact PCImage as pro on this forum
- he is from UK - Peterborough....

For your datas safety - double check before, ask a pro, and only afterwards start any action.

+++

@falther hi, yes its set up as RAID 1 (mirror) mode and still working great. The unit i have is made by Buffalo and i bought it to replace some older Buffalo units i have. The main adavantage it has is being USB3 so its super fast compared with the older USB2 unit. Of the older Buffalo units i have (3 off!) at least 2 of them have power problems. I found that leaving the power switch in the ON position and switching on at the plug socket has more success of the unit powering up. The older units have 500GB hard drives in them. Yes i'm aware that NAS drives are slower but this won't be for my main drive. I will probably copy the data off the ext Buffalo drive to an internal SATA drive as that will be quicker..i don't have any USB3 external boxes to house hard drives.

In order to support Windows XP, some external drives are configured with larger sector sizes (eg 4KB) while others are configured to enumerate as two or more "virtual" physical drives. To determine whether you have two partitions or two physical drives, you could examine the drive with a disc editor (eg DMDE freeware). DMDE can also identify whether the sector size is something other than 512B.

Alternatively you can query the sector size as follows:

viewtopic.php?f=1&t=28346

If the external drive is configured as two virtual physical drives, then I suspect it may have a normal MBR at sector 0 and a second MBR at the first sector beyond the 2TiB point. If you attach such a drive via SATA, then Win XP will see the 2.2TB drive but not the remaining 800GB. To see the latter, you may be able to use the Extended Capacity Manager that is included with Acronis True Image (or Seagate's free DiscWizard, an OEM version of Acronis True Image).

Of course you will need to ensure that the SATA driver is not affected by a 32-bit LBA limitation.

_________________
A backup a day keeps DR away.