I have a spanned volume (3x6+ TB disks spanned to one 20+ TB volume) that I need to mirror or clone to a new 20+ TB (unspanned) volume. Once mirrored or cloned I'm going to destroy the original volume and reuse the storage elsewhere.
Windows 2008 will not allow me to mirror it because the original is a spanned volume.
I cannot simply copy the data, because there are sparse files on the volume. So the OS thinks there is 150+ TB used on the disk when there really is only around 18TB used physically. When I try to use the copy command it won't run because it thinks the destination volume needs to be 150+ TB to hold it all.
A conundrum, but I figure someone here has the answer.
Use Microsoft robocopy - it will do whatever you need.
I had this same question. According to Microsoft, you can't mirror a spanned volume:
Using spanned volumes
Caution:
I was hoping to use mirroring as a way to perform a SAN migration, but it looks like it's a no-go. Depending on the dataset, Robocopy may not be a great choice. If you're running Exchange or SQL, Robocopy works at the file level. Once those DBs are mounted, they're changed and Robocopy would have to re-copy the entire file. Kinda sucks if the DB is like 4TB. That's a long offline copy.
One thing I did notice is you can shrink a volume. I didn't see a way to dictate which volumes you could remove, but I was able to extend my mirror to 4 different disks and shrink the mirror to the 1st disk. I could mirror then, but depending on how large your dataset is, this may not be a good choice.
You might look into Acronis to see if it's "Disk Director" will manage your existing partitions/volumes. If so, it may be able to resize the existing partition/volume while copying it over to the new configuration.