On Tue, Mar 14 2017, Alfred Matthews wrote:

>> Does
>>   dmraid -b /dev/sda /dev/sdb /dev/sdc
>> tell you anything useful?
>>
>
> # dmraid -b /dev/sdb /dev/sdc
> /dev/sdc:   5860533168 total, "WD-WCAWZ2927144"
> /dev/sdb:   5860533168 total, "WD-WCAWZ2939730"


No, not useful.

Your other output also doesn't show anything interesting.
I had another look at the lsdrv output you showed before and I'm
wondering if there really is anything "hardware RAID" here at all.

Both drives (sdb and sdc) are partitioned into a 200MB EFI partition, a
2.75TB hfsplus (Apple file system) / unknown partition, and a 128M
hfsplus boot partition.

Maybe the two 2.75TB paritions were raided together.
sdc looks like the "first" device if this were the case.
Try:

  mdadm --build /dev/md0 --level=0 -n2 --chunk=512M /dev/sdc2 /dev/sdb2

Then try fsck.hfs of hpfsck ... in the "hfsplus" package on Debian.
 hpfsck /dev/md0
maybe.

NeilBrown