On 25/11/2022 13:30, David T-G wrote:
% Either version (10, or 1+0), gives you get the speed of striping, and the
% safety of a mirror. 10, however, can use an odd number of disks, and disks
% of random sizes.
That's still magic to me 😄 Mirroring (but not doubling up the
redundancy) on an odd number of disks?!?
Disk: a b c
Stripe: 1 1 2
2 3 3
4 4 5
5 6 6
and so on.
I was trying to work out how I'd smear them a lot more randomly, but it
was a nightmare. Iirc, no matter how many drives you have, (for two
copies) it seems that drive a is only mirrored to drives b and c, for
any value of a. So if you lose drive a, and then either b or c, you are
guaranteed to lose half a drive of contents.
It also means that replacing a failed drive will hammer just two drives
to replace it and not touch the others. I wanted to try and spread stuff
far more evenly so it read from all the other drives, not just two.
Okay, it increases the risk that you will lose *some* data to a double
failure, but reduces the *amount* of data at risk (and also reduces the
risk of a double failure!). Because if the first failure *provokes* the
second, data loss is pretty much guaranteed.
Cheers,
Wol
