On Wed, Jul 18, 2018 at 08:39:48AM +0000, Duncan wrote: > Duncan posted on Wed, 18 Jul 2018 07:20:09 +0000 as excerpted: > > >> As implemented in BTRFS, raid1 doesn't have striping. > > > > The argument is that because there's only two copies, on multi-device > > btrfs raid1 with 4+ devices of equal size so chunk allocations tend to > > alternate device pairs, it's effectively striped at the macro level, > > with the 1 GiB device-level chunks effectively being huge individual > > device strips of 1 GiB. > > > > At 1 GiB strip size it doesn't have the typical performance advantage of > > striping, but conceptually, it's equivalent to raid10 with huge 1 GiB > > strips/chunks. > > I forgot this bit... > > Similarly, multi-device single is regarded by some to be conceptually > equivalent to raid0 with really huge GiB strips/chunks. > > (As you may note, "the argument is" and "regarded by some" are distancing > phrases. I've seen the argument made on-list, but while I understand the > argument and agree with it to some extent, I'm still a bit uncomfortable > with it and don't normally make it myself, this thread being a noted > exception tho originally I simply repeated what someone else already said > in-thread, because I too agree it's stretching things a bit. But it does > appear to be a useful conceptual equivalency for some, and I do see the > similarity. > > Perhaps it's a case of coder's view (no code doing it that way, it's just > a coincidental oddity conditional on equal sizes), vs. sysadmin's view > (code or not, accidental or not, it's a reasonably accurate high-level > description of how it ends up working most of the time with equivalent > sized devices).)
Well, it's an *accurate* observation. It's just not a particularly *useful* one. :) Hugo. -- Hugo Mills | I gave up smoking, drinking and sex once. It was the hugo@... carfax.org.uk | scariest 20 minutes of my life. http://carfax.org.uk/ | PGP: E2AB1DE4 |
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