Hello,
as changes to the softraid metadata format have been brought up on tech@
recently, it may be a suitable time now to mention one my concern. It is
sector size unrelated, but I think it would be wise to think about it when
you plan changes to the metadata format now or in the future.
There is only one copy of the metadata in each chunk. That means that
there is only one copy of the encryption key(s) in a CRYPTO volume. You
probably already understand where I am aiming - sectors do fail from time
to time, other bad things do happen. In my opinion if filesystems have
backup copies of superblocks, there are copies of MBR, msdos filesystems
have copies of FAT, etc, it would be foolish to have only one instance of
the encryption key(s). Loss of encryption key(s) can't even be compared to
a loss of a superblock or of a partition table. Word 'worse' would not
describe that situation sufficiently.
I'm paranoid enough to manually make copies of the metadata and to store
them somewhere else. Nonetheless I think that a little space at the very
end of each chunk is a suitable candidate to be reserved for storing a
metadata backup automatically there. It would make the data area very
slightly shorter. Area at the end of the chunk has a better chance to
survive an incident at the beggining of the chunk (the area where actual
metadata is stored) than an area somewhere nearby it.
I'm well aware that this is only a talk from me and no code, but since
there are changes to the metadata format in progress I want to bring your
attention to this topic now. If that or maybe a different area is reserved
beforehand, some metadata version bumps and other issues can be avoided in
the future.
Thank you.
Regards,
David
