Andrei, et al --
...and then Andrei Borzenkov said...
%
% On Thu, Mar 1, 2018 at 12:37 PM, Wols Lists wrote:
...
% > Raid-6 is still fully redundant with one failed drive. If you mirror it
% > to raid-61, that means you can lose at least four drives and still not
% > lose data.
%
% If you mirror it, you can lose half of all drives.
[snip]
Well, hold on...
You could either mirror each drive A1-A2, B1-B2, C1-C2, ... and then
stripe all #1 into array 1 and mirror it onto array #2, and that would
indeed give you the ability to lose many drives. You might even simply
mirror A1-A2, B1-B2, C1-C2, ... and then build a large volume from each
of those mirrored devices.
But if you create your large array #1 first using RAID whatever and
then create another #2 and mirror that way, then you can lose only the
redundancy from each side before losing the entire stripe (#1 or #2).
In the worst case, if it were RAID 0, then losing a single drive would
destroy the array.
So do you mirror and then stripe, or do you stripe and then mirror?
How many drives you can lose where will be different depending on the
approach.
This has all been delightfully fascinating for me, one of those sad
household users stuck behind a small pocketbook :-)/2 Thank you all!
HTH & HAND
:-D
--
David T-G
See http://justpickone.org/davidtg/email/
See http://justpickone.org/davidtg/tofu.txt
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