My Cloud Ex2 Ultra - Will adding 2nd drive (SPAN) erase drive 1?

I have an Ultra EX2 with one 8TB drive that is about 75% full. I added a 2nd 8TB drive and was going to configure it in SPAN mode so it appears as one large 16TB drive, however I got a warning that both drives will be erased. Is this correct, why would drive 1 be erased when in Span mode when one drive is full, it spills over to writing onto the 2nd? Thanks

Hi @stanmarlin,

Please contact the WD Technical Support team for best assistance and troubleshooting:

This is because if you started off with a single drive, it would probably have been setup in JBOD (single disk) mode. Attempting to add another drive and switching to Span (RAID linear) mode (or any other mode) requires the filesystem and mapping for both drives to be reset, so the NAS is forced to erase the first drive if you wish to proceed.

In any case, Spanning (and RAID 0) are risky to use for drives as large as yours. Losing a single drive in either of these setups would mean a total loss of 16TB of data (you may be able to recover something in span mode but the chances are very low). It is advisable to continue using JBOD for both drives instead.