On Mon, Feb 20, 2012 at 08:59:05PM -0500, Tom Cameron wrote: > Gareth, > > I would completely agree. I only use the RAID vernacular here because, > well, it's the unfortunate defacto standard way to talk about data > protection. > > I'd go a step beyond saying dupe or dupe + stripe, because future > modifications could conceivably see the addition of multiple > duplicated sets. The case of 4 disks in a BTRFS filesystem with dupe > running across all of them would be a clear extension I could see. So > that would be something like 4D. I'm not real sure what you'd use for > the terminology, but something completely different than RAID-like > terms is almost certainly best. Just look at the ZFS documentation to > see how carefully they have to spell out what RAID-Z, Z2, and Z3 do > because they used the RAID acronym. /me opens a plate to put the can of worms on. Some time ago, I proposed the following scheme: <n>C<m>S<p>P where n is the number of copies (suffixed by C), m is the number of stripes for that data (suffixed by S), and p is the number of parity blocks (suffixed by P). Values of zero are omitted. So btrfs's RAID-1 would be 2C, RAID-0 would be 1CnS, RAID-5 would be 1CnS1P, and RAID-6 would be 1CnS2P. DUP would need a special indicator to show that it wasn't redundant in the face of a whole-disk failure: 2CN Hugo. > On Mon, Feb 20, 2012 at 8:47 PM, Gareth Pye <gareth@xxxxxxxxxxxxxx> wrote: > > On Tue, Feb 21, 2012 at 12:07 PM, Tom Cameron <tomc603@xxxxxxxxx> wrote: > >> > >> It seems from the BTRFS documentation that the RAID1 profile is > >> actually "mirror", or store 2 copies of the object. Perhaps when > >> Oracle makes BTRFS a production option they should more clearly spell > >> that out. > > > > > > I'd really like BTRFS to not use RAID level terminology anywhere (other than > > maybe in parenthesis along the lines of: "this is similar to RAIDX") and use > > less ambigious options as the recommended way to talk about things. As there > > is good reason to talk about Dup and RAID1 differently as they aren't the > > same on more than 2 drives. Doing it that way will make people understand > > what is going on more often, which should be good. > > > > It also makes things much easier to remember. Like how much data can you fit > > on a 6 drive RAID10? I dunno, but I can more intuitively answer that same > > question when it is phrased as just simply 'dup', or maybe 'dup + stripe'. > > > > Is there a difference in BTRFS between dup and raid10? > > -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- Great oxymorons of the world, no. 4: Future Perfect ---
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