Adding a hotspare to a pool: can I remove it afterwards?

TrueNAS General
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Due to a series of unfortunate events, I purchased 2 16TB HDDs and discovered I don’t need them anymore (the HDDs that were meant for replacement are not actually broken).

I don’t want these HDDs to go bad, so my thought was to put them as hot spare of other pools.

I have 2 pools, each pool is made in the following way:’

1 pool of 1 vdev. The vdev is a mirror (2 disks set up as a mirror vdev).

When trying to add a hot spare, it looks like I have to add another vdev to the pool and set this vdev as hotspare.

If I want to later remove the hotspare because maybe the pool is on it’s fine and a different pool breaks, will the hotspare vdev cause problems? I remember that removing a vdev from a pool usually breaks stuff.

I have no experience with more than 1 vdev, so I’m not sure about the consequence of this operation. All I want is my HDDs to spint and minimize their hardware “consumption” but prevent them to die by being on a shelf.

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You can remove spares after they are added, yes. It’s not an issue.

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And pools can share hot-spares.

Of course, whence a hot-spare is needed, it becomes tied to the pool needing it. It becomes free again after the failed disk has been replaced.

Note that you can cause a hot spare to permanently replace a failed disk, if that is desired.

Last, sharing hot spares prevents one pool from being exported independent from the other.

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Even if the hot spare is not currently being used by any pool?

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Good point, I looked it up in the manual page for “zpoolconcepts”;

   If  a  pool  has a shared spare that is currently being used, the pool cannot be exported, since other pools
   may use this shared spare, which may lead to potential data corruption.

That implies that a pool can be exported with shared hot spare that is not in use.

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This is exactly what I want. I tried to do this through the UI on TrueNAS core, but I can’t seem to be able to use the same disk for multiple vdevs and I can’t figure out how to assign the “hot spare” vdev to multiple pools

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The GUI does not always expose all the features of ZFS.

It also helps to use the right terminology. This wording;

but I can’t seem to be able to use the same disk for multiple vdevs

Should probably be written;

but I can’t seem to be able to use the same disk for multiple pools

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I see, I might stick to just one hotspare per pool. I have 3 mirrors on one pool, and 2 other pools and 2 spares, so I can just have 1 hot spare for the other pool.

Thank you!