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Probably stupid questions but here goes:

  1. Can btrfs use only a portion of a HDD in a raid "array"?

  2. I have 3 HDDs: 80GB, 160GB, and 200GB external USB. I want to put root+boot in the first 20GB of the smallest drive on EXT4 and use the rest of the free space on all 3 drives for a btrfs "raid10 array". Is this possible?

  3. Is this sane? Would you do it differently?

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1) Yes
2) Yes
3) Seems sane to me.

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I'm at the point of running "sudo mkfs.btrfs -m raid10 -d raid10 /dev/sda2 /dev/sdb /dev/sdc" but it doesn't honor sda2. I'm hesitant to just put sda because I have not read anything indicating it'll leave current partitions on the drive alone. Further, certain man pages mention options for specifying which block to start at and starting at zero by default. – bumbling fool Feb 9 '11 at 20:22

1) Yes, but this can cause problem's in the earlier versions of the FS (pre may 2011).
2) Although this can be done, in hindsight, I should have either used all drives in an array with /boot and everything else on there, or added another smaller driver for /boot & /root
3) Not really... See 2

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re:2, why was this bad? (ie, edit your answer to explain why) – djeikyb Mar 18 '11 at 22:01

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