On Wed, Feb 22, 2012 at 11:22:08AM +0100, Hubert Kario wrote: > On Wednesday 22 of February 2012 09:56:27 Xavier Nicollet wrote: > > Le 21 February 2012 ? 07:54, Hugo Mills a écrit: > > > 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 > > > > Seems clear. However, is the S really relevant ? > > It would be simpler without it, wouldn't it ? > > It depends how striping will be implemented. Generally it provides > information on how much spindles is the data using. With static > configuration it will be useless, but when you start changing number of > drives in set then it's necessary to know if you're not under- or over- > utilising the disks. Indeed. If the implementation always uses the largest number of devices possible, then we'll always have nS. If it allows you to set a fixed number of devices for a stripe, then the n will be a fixed number, and it becomes useful. Hugo. -- === 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 --- Happiness is mandatory. Are you happy? ---
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