SSD drives work differently from ordinary hard drives. When the drives/array was reformatted, the OS probably sent a huge number of "
trim" commmands to both drives, telling them that all the sectors previously allocated to various files are no longer in use.
That means the drive can ignore the contents of those sectors when another sector in the same erase block has to be rewritten, which increases performance, but it also means the drive may choose to return a fake response containing only zeroes to any read request for those sectors.
Some drives do this, others don't; it all depends on the firmware. If you can't find any data using tools like TestDisk or PhotoRec, that indicates pretty strongly that only zeros are being returned. If so, the
dd operation is likely to result in an almost completely blank destination disk.
You could try reading a few random sectors from the beginning of the array with
dd (or read directly from one of the array members with
hdparm); you should not have to try many sectors before seeing random data. If you keep getting sectors that are all zeroed-out, you will need to contact the drive manufacturer for further advice.