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I have 4 disks, 2 of 500GB, 1 of 1TB e 1 of 2TB capacity. I would like to create a striped array from first 3 disks (500GB + 500GB + 1TB), then mirror the content on 2TB disk. It's possible? I would do this using btrfs capabilities.

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It seems that what you are looking for is a hybrid RAID 0+1. It's possible but it wouldn't work exactly in the way that you want it to.

The only way to get exactly what you want would be to have four disks of the same capacity so that the first two disks would be striped and then mirrored by the other two disks which would also be striped or to have some of the stripes mirrored onto the fourth disk.

In your case, it wouldn't be possible to mirror the content from the first three disks to the fourth disk as it doesn't function that way. The best thing that you could do is to stripe the first three disks and then create a backup of the data from the first three disks onto the fourth disk but it wouldn't be a mirror, per se.

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  • I also thought of creating a logical device from three drives (done with LVM), then creating btrfs filesystem with mirroring between logical device and 2TB disk
    – user844519
    Dec 3, 2017 at 21:23
  • That would work if you just wanted to have the data from the first three drives backed up onto the second drive but it wouldn't work in the way that you want it to. The data on the LV would be written across the three disks but it wouldn't be striped as it is in a RAID 0 array so it wouldn't give any enhanced performance which is the purpose of striping. It also wouldn't be possible to mirror it because you'd have to create the RAID 1 first which isn't possible because your disks aren't of the same size.
    – Nasir Riley
    Dec 4, 2017 at 3:24

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