On Sun, Jul 01, 2012 at 01:50:39PM +0200, Waxhead wrote: > As far as I understand btrfs stores all data in huge chunks that are > striped, mirrored or "raid5/6'ed" throughout all the disks added to > the filesystem/volume.
Well, RAID-5/6 hasn't landed yet, but yes. > How does btrfs deal with different sized disks? let's say that you > for example have 10 different disks that are > 100GB,200GB,300GB...1000GB and you create a btrfs filesystem with > all the disks. How will the raid5 implementation distribute chunks > in such a setup. We haven't seen the code for that bit yet. > I assume the stripe+stripe+parity are separate chunks that are > placed on separate disks but how does btrfs select the best disk to > store a chunk on? In short will a slow disk slow down the entire > "array", parts of it or will btrfs attempt to use the fastest disks > first? Chunks are allocated by ordering the devices by the amount of free (=unallocated) space left on each, and picking the chunks from devices in that order. For RAID-1 chunks are picked in pairs. For RAID-0, "as many as possible" are picked, down to a minimum of 2 (I think). For RAID-10, the largest even number possible is picked, down to a minimum of 4. I _believe_ that RAID-5 and -6 will pick as many as possible, down to some minimum -- but as I said, we haven't seen the code yet. > Also since btrfs checksums both data and metadata I am thinking that > at least the raid6 implementation perhaps can (try to) reconstruct > corrupt data (and try to rewrite it) before reading an alternate > copy. Can someone please fill me in on the details here? Yes, it should be possible to do that with RAID-5 as well. (Read the data stripes, verify checksums, if one fails, read the parity, verify that, and reconstruct the bad block from the known-good data). > Finaly how does btrfs deals with advanced format (4k sectors) drives > when the entire drive (and not a partition) is used to build a btrfs > filesystem. Is proper alignment achieved? I don't know about that. However, the native block size in btrfs is 4k, so I'd imagine that it's all good. 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 --- You stay in the theatre because you're afraid of having no --- money? There's irony...
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