OK, the way WHS manages disks is the following:
The primary drive that the OS is installed on is partitioned so that the OS sits in a 20Gb partition and the remainder of the space is called DATA on drive D. The size of this D drive will not change by adding more drives and is the reason why it is recommended to have the largest hard drive your primary (to make this D drive as big as possible, more on this below).
If you have just the single hard drive in WHS, then all backups and files that you put on WHS shares are on this DATA partition and you have no possibility of folder duplication (as there is only one drive).
If you have two hard drives, the disk extender software (DE) will move off as much data as it can onto the second hard drive to balance out space and so forth. Now, you should note that the second hard drive (and any subsequent drives- 3rd, 4th, etc) will not appear in my computer- this is by design
The other hard drives are there (see the console) and you can look at their free space (if you desire) under Disk Management in Computer Management (on the server go to Start>Control Panel>Administrative Tools>Computer Management and then click on Disk Management - about halfway down the left hand list). In Disk Management you can see that the 2nd (& 3rd, 4th, etc) hard drives are also called DATA but have no drive letter/label (i.e. are not E, F & G drive under My Computer)
What happens is that as you copy data to the shares, they get stored on the DATA partition that you see in My Computer. DE will then move off files off of the D drive onto the second hard drive (or making duplicates if duplication is switched on for that folder). If you copy files to the WHS shares at a faster rate than what DE will move them off then you will reach the point where the DATA D drive will get down to less than 5Gb which is when you get your warnings.
What you need to do is wait for DE to move files off onto the second hard drive, freeing up space on the primary DATA partition (the one you see in My Computer). Then you can copy more files over which will get temporarily stored on the DATA partition until they are moved off.
It is a similar situation with 3 or more drives but DE will basically try to make the DATA D drive as empty as possible, duplicating among the extra 2 drives where necessary and only containing the reparse pointers (don't worry if you don't know what this means; they point, kind of like shortcuts, to where DE has moved/stored the file on other hard drives).
You should note that the total free space that WHS reports in the console includes the primary data partition. It works it out by totalling all available hard drive capacity, subtracts the 20gb system partition and then any used space (for backups, files and duplicated files).
So, if you understood all of that, that is why WHS reports you have only 5gb remaining when WHS console reports 100+ gb free space; you have overloaded the DE migration and need to wait for the files to be moved off the primary drive.
If it hasn't done so already, the warning will disappear and you'll see the free space of the D drive in My Computer get larger as files are moved off.
So, simple answer, just wait for WHS to do its thing. Think of it that yo can only copy so many Gb's to the server at any one time.
Hope you're still with me after all that,
Davo
