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zfs:raid:stripe

ZFS Stripe/Span

Basically a junction of 2 or more drives or other vdev shapes.

When created together, with equal capacity, ZFS space-balancing makes a span act like a raid0 stripe.

Basically, the space is added together. That's the important point.

Basically, a stripe occurs where all the devices/vdevs are initialized into the pool simultaneously.

Provided all the devices are of the same size, the stripe behavior will continue regardless of fullness level.

If devices/vdevs are not equally sized, then they will fill mostly equally until one device/vdev is full. The stripe behavior stops at that point and the other device(s)/vdev(s) with more capacity will be used more.

A span occurs where the pool starts with a certain number of devices or vdevs and more devices or vdevs are added later. The newer-added devices start empty. ZFS makes no effort to balance the data in the pool across those devices or vdevs. This is not a design flaw. As more data is copied to the pool ZFS will start filling with the least full device/vdev to a point where the devices/vdevs are roughly equally full. Once all devices/vdevs are roughly equally full, it will start to behave in a stripe-like behavior.

While behaving in a stripe-like manner, here are some pros and cons:

Pros:

  • Reading and/or writing can be significantly faster - reading or writing simultaneously to multiple devices is faster than using a single device
  • Drives/vdevs don't have to be used singularly - more combined space

Cons:

  • Lack of redundancy - If the underlying vdevs don't include redundancy, one drive failure can result in even more data loss than you might anticipate. For example, with a stripe of 3 devices/vdevs, and one device/vdev fails, at best, any file that had portions stored on the failed device will have chunks missing, and at worst, the whole pool will be unsalvageable.

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