openzfs / zfs

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This feature allows disks to be added one at a time to a RAID-Z group, expanding its capacity incrementally. This feature is especially useful for small pools (typically with only one RAID-Z group), where there isn't sufficient hardware to add capacity by adding a whole new RAID-Z group (typically doubling the number of disks).

For additional context as well as a design overview, see my upcoming talk at the 2021 FreeBSD Developer Summit (June 11, 2021).

A new device (disk) can be attached to an existing RAIDZ vdev, by running zpool attach POOL raidzP-N NEW_DEVICE, e.g. zpool attach tank raidz2-0 sda. The new device will become part of the RAIDZ group. A "raidz expansion" will be initiated, and the new device will contribute additional space to the RAIDZ group once the expansion completes.

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