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I have been googling for a while and have not found definitive answer.

I saw Btrfs mirroring chunks of data and not exactly a whole-drive mirror like a traditional RAID. Now assume I have 8 1TB drives in a single RAID1 pool of Btrfs. Does this mean I can theoretically lose even 4 drives without losing any data (losing 1 drive per mirrored pair)? And if it were 7 drives can I lose as many as three?

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According to the btrfs wiki:

NOTE This does not do the 'usual thing' for 3 or more drives. Until "N-Way" (traditional) RAID-1 is implemented: Loss of more than one drive might crash the array. For now, RAID-1 means 'one copy of what's important exists on two of the drives in the array no matter how many drives there may be in it'.

If this is to be believed then losing 4 drives will definitely crash the array.

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  • So there's no way to make it save 3 copies?
    – endolith
    Commented Feb 15, 2019 at 5:44
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    Currently not. If you have a 3+ disk setup and need that level of redundancy then you can look into using ZFS with its various RAID levels that can allow for better disk redundancy. Example: 3 drives using ZFS RAIDZ2 will allow two disks to fail while still keeping your data intact.
    – Hermanio
    Commented Feb 16, 2019 at 19:29

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