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Comment by Nican | Hacker News Reader

dRAID looks really fascinating, but presentation is pretty abstract. Would it allow to add/remove drives from a pool, and allow ZFS to rebalance itself?

Would be great for home use, where I have a lot of drives that I collected over the years that are not the same size.

EDIT: The more I read into this, it still seems assume that all drives must be of the same size.

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I don't think so. The essence of draid is that, instead of keeping a spare drive unused in case one of the working drives fail, it incorporates the spare drive to the array and uses it, but one drive worth of free space is reserved randomly across the entire array.

That way, if one disk fails, the reserved space is used to write the data necessary to keep the array consistent. Because the free space is distributed randomly across the array, the write performance of a single drive doesn't become a bottleneck.

This is unrelated to the ability to remove drives from a pool (which is difficult to support in ZFS due to design constraints)

Maybe this presentation by Mark will help?

dRAID, Finally![0]

[0]: https://www.youtube.com/watch?v=jdXOtEF6Fh0

This sounds like synology hybrid raid, which uses lvm and mdadm together for something similar if I recall.

You can already do that with btrfs.

I currently use btrfs with RAID1 at home, and it works great. But btrfs also does not have the track record for being the most stable filesystem as compared to ZFS.

[1] https://lore.kernel.org/linux-btrfs/20200627032414.GX10769@h... [2] https://lore.kernel.org/linux-btrfs/20200627030614.GW10769@h... [3] https://lore.kernel.org/linux-btrfs/20200520013255.GD10769@h...

You can do that with ZFS too, at least for mirrored sets (i.e. RAID10). It's possible to remove a vdev, and the pool will migrate the data to the remaining vdevs.

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