[clue] btrfs vs ZFS question

[Shawn Perry]

I’m assuming you mean me, so I’ll answer.

1. You can add. You should add in the same pattern that already exists to maintain performance and redundancy. If you have a 4 disk raid 5, you should add 4 more disks in a raid 5 config.
a. You cannot remove yet. 0.8x will allow removing, but only to cover accidental adds.
2. You can resize up. If you replace a disk with a larger one, you can expand the space. If you add more disks, you can use the extra space.
a. You cannot shrink or remove.
3. The data does not need balancing unless you add disks. To rebalance, you would need to re-copy the data. You can use send/recv to do that. You’d need to stop things to do this. The actual stoppage will be only the amount of time it takes you to type “zfs rename <source> <destination>” twice. Once to move the old out of the way, once to move the new back to the original location.
4. Sorta. You can split mirrors in a raid 1 or raid 10 config to drop down to a single disk or raid 0, respectively. You cannot reshape like md or btrfs.

From: Dennis J Perkins
Sent: Wednesday, March 27, 2019 9:23 PM
To: CLUE's mailing list
Subject: [clue] btrfs vs ZFS question

Sean, does ZFS let you do these things?

Btrfs lets you do the following without stopping anything:

1. Add or remove partitions.  If you remove a partition, make sure the
remaining drives have enough capacity.
2. Resize a btrfs system.
3. Balance the data.
4. Switch between single disk, RAID 0, RAID 1, or RAID 10 configs.

Shuffling data around as a result of any of these operatins is done in
the background and might take hours.

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