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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.

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Use Microsoft robocopy - it will do whatever you need.

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I had this same question. According to Microsoft, you can't mirror a spanned volume:

Using spanned volumes


Spanned volumes cannot be mirrored and do not offer fault tolerance. If one of the disks containing a spanned volume fails, the entire volume fails and all the data on it is lost.*

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.

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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.

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I should have mentioned that it needs to be a free solution. It also has to work while Windows is running, so gparted or Partition Magic typesolutions won't work. Since the volume is spanned by Windows, I don't think any solution that runs apart from Windows will work. – Matt Aug 17 '11 at 15:16
"it needs to be a free solution" you may be out of luck there as there are solutions which run within a running Windows session, but most of them (maybe all) are not free. – user48838 Aug 17 '11 at 15:25

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