On 07/17/2018 11:12 PM, Duncan wrote: > Goffredo Baroncelli posted on Mon, 16 Jul 2018 20:29:46 +0200 as > excerpted: > >> On 07/15/2018 04:37 PM, waxhead wrote: > >> Striping and mirroring/pairing are orthogonal properties; mirror and >> parity are mutually exclusive. > > I can't agree. I don't know whether you meant that in the global sense, > or purely in the btrfs context (which I suspect), but either way I can't > agree. > > In the pure btrfs context, while striping and mirroring/pairing are > orthogonal today, Hugo's whole point was that btrfs is theoretically > flexible enough to allow both together and the feature may at some point > be added, so it makes sense to have a layout notation format flexible > enough to allow it as well.
When I say orthogonal, It means that these can be combined: i.e. you can have - striping (RAID0) - parity (?) - striping + parity (e.g. RAID5/6) - mirroring (RAID1) - mirroring + striping (RAID10) However you can't have mirroring+parity; this means that a notation where both 'C' ( = number of copy) and 'P' ( = number of parities) is too verbose. [...] > >> Question #2: historically RAID10 is requires 4 disks. However I am >> guessing if the stripe could be done on a different number of disks: >> What about RAID1+Striping on 3 (or 5 disks) ? The key of striping is >> that every 64k, the data are stored on a different disk.... > > As someone else pointed out, md/lvm-raid10 already work like this. What > btrfs calls raid10 is somewhat different, but btrfs raid1 pretty much > works this way except with huge (gig size) chunks. As implemented in BTRFS, raid1 doesn't have striping. -- gpg @keyserver.linux.it: Goffredo Baroncelli <kreijackATinwind.it> Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
