External USB Drive not keeping assigned drive letter

[stgrimes]

I am using three (3) external USB hard drives (they are identical) to back up my critical files. I am using backup software with the USB drives as the target. I rotate these drives each week to maintain off-site backup, etc.

My problem is that XP Pro will not "remember" the drive letter I have assigned to these drives. I used disk management to assign drive "z" for these drives. However, when I rotate the drives the next week, the drive comes up as "h" or whatever the next drive is depending on whether I have my flash drive plugged in.

I have assigned "z" to all three hard drives individually with no change. They worked great for several months then started this nonsense.

Any suggestions?

[Mobo]

So the flash drive is the issue. If you pplug in all drives one at a time without the flash drive do they identify properly ?

Also if you hookup a hard drive and get z for it, then attach a flash drive what does that use for a drive letter ?