On Thu, May 03, 2012 at 01:56:10PM +0700, Fajar A. Nugraha wrote: > On Thu, May 3, 2012 at 1:46 PM, Chu Duc Minh <[email protected]> wrote: > > Hi, i have some questions when using Btrfs on multi-devices: > > 1. a large file will always be stored wholely on a device or it may > > spread on some devices/partitions? > > IIRC: > - in raid1 mode, it will be written on all disks (or was it TWO disks, > regarless how many device in a mirror? can't remember which).
Any given block of the file will appear on two disks. There's no guarantee that all the blocks of a file will be stored on the same two disks, though. > - in raid10 and raid0, it will always be spread, on a minimum of two devices Again, any given block of a file will appear on precisely two disks (for RAID-10), or precisely one disk (for RAID-0). However, for a sufficiently large file (i.e. multiples of the stripe size, which is 64KiB, I think), the blocks will be spread across all disks. If the file is highly fragmented, this is a statistical statement; if the file is contiguous, it is a guarantee. 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 --- Ceci n'est pas une pipe: | ---
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