After an experimental phase tuning my then-new Sisyphus NAS build (for 10gigE speed and capacity), I ended up with 3 vdevs of 3x4TB RAIDZ1 for my pool, plus I had a couple of spare slots and drives so popped another two drives in and set them as Spares to the pool.
Whenever ZFS decides to kick out a drive, one of the Spares hops in and takes care of things until I replace the ejected drive. While this is happening the pool is Degraded, not Resilvering. The Spare isn't being used to take the place of the ejected drive like a Replace would. When I Replace the ejected drive with a new one the pool Resilvers as expected.
I originally added the spares because I had literal spare drives and expected them to swap in directly on a fail. That's not what happens.
What's the Spare doing, exactly?
Is there any point in me having them?
Are they actually protecting against a type of failure that could follow after the original drive ejection? I'm certain that if another disk in a VDEV failed I'd lose the pool, so it's not protective in the usual RAIDZ redundancy sense.
Have I just missed this in the FreeNAS docs somewhere, because I can't find much chat about ZFS Spares on the web at all.
Whenever ZFS decides to kick out a drive, one of the Spares hops in and takes care of things until I replace the ejected drive. While this is happening the pool is Degraded, not Resilvering. The Spare isn't being used to take the place of the ejected drive like a Replace would. When I Replace the ejected drive with a new one the pool Resilvers as expected.
I originally added the spares because I had literal spare drives and expected them to swap in directly on a fail. That's not what happens.
What's the Spare doing, exactly?
Is there any point in me having them?
Are they actually protecting against a type of failure that could follow after the original drive ejection? I'm certain that if another disk in a VDEV failed I'd lose the pool, so it's not protective in the usual RAIDZ redundancy sense.
Have I just missed this in the FreeNAS docs somewhere, because I can't find much chat about ZFS Spares on the web at all.
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