To my understanding, as the data size did not exceed 2TB, the
files should all be stored on the first disk, so theoretically I shouldn't have
lost any data.
This may not necessarily be true. The filesystem is merely a set of data
structures that describe a single, logical pool of blocks that in your case
spanned two physical devices. Although most filesystems tend to fill up those
blocks in order from lowest to highest, they can in theory allocate any free
block for data storage. Different filesystems use different metrics in their
decision-making process of which blocks to allocate, but depending on the age of
the filesystem and the options used to format it, the data could be fragmented
across both disks with some pieces winding up on the other drive that has
failed. This applies regardless of whether you're using hardware or software
If the drive was mostly used for data storage with lots of files that did not
change very frequently, then there is a good chance that they could all be
intact on the first drive. But if the JBOD was used as scatch space or an OS
boot drive with lots of small random writes happening a lot of the time, there
is a higher likelihood that some of that data you wish to recover is now lost.
I tried mounting the first HDD alone but no option combination of mount had
That is to be expected. The filesystem headers (if mount can even locate them)
describe a layout that is radically different than what a single disk would
show. Also, half of the filesystem descriptors, inodes, or whatever (depending
on the filesystem) are on that failed disk, so those two things add up to a
whole lot of bad/missing/corrupt filesystem metadata that mount can't handle.
Your only hope here is to use data recovery software. This will be difficult
because most data recovery software tries to focus on repairing the filesystem
itself, but as discussed, yours is likely destroyed beyond
- This is the danger of running JBOD. Keep them backed up.