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In short, raidz is ZFS answer to raid5/6. The basic raidz construct requires 2 or more drives for data and 1 or more (up to 3) drives for parity. The number of parity drives is typically appended to raidz when describing the construct. For example, raidz with one parity drive is raidz1 (often just truncated to raidz), with 2 parity drives, it is raidz2, and with 3 parity drives, it is raidz3.

For optimum performance, it is recommended to use the formula (2^x + p). In this calculation, “p” is number of parity drives, and 2^x is the recommended optimal number of data drives.

Examples: (just examples, using the formula, any variation can exist)

  • 3-way raidz - 2 data drives, and 1 parity drive.
  • 5-way raidz - 4 data drives, and 1 parity drive.
  • 6-way raidz2 - 4 data drives, and 2 parity drives.
  • 9-way raidz - 8 data drives, and 1 parity drive. (somewhat not recommended because with just a second drive failure, the entire pool content could be rendered unsalvageable)
  • 11-way raidz3 - 8 data drives, and 3 parity drives.

Sub-optimal variations can be used, and ZFS will do its best to make them work.

These vdevs can also be striped.

Some common shapes are:

  • 2x 3-way raidz - 6 drives total, 2 used for parity, either vdev can suffer 1 drive failure before losing data. This shape should probably instead just be a 1x 6-way raidz2.
  • 3x 6-way raidz2 - 18 drives total, 6 used for parity, any particular vdev can suffer up to 2 drives of failure before losing data.

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zfs/raid/raidz.txt · Last modified: 2018/07/08 16:57 (external edit)