Adding metadata vdev/fusion pool to an existing pool

[winnielinnie]

@user0241233

Does each data vdev requires its own metadata vdev or each pool requires one metadata pool only?

Each pool. It’s a pool-wide vdev.

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@user0241233

can I create a metadata vdev for a data vdev that has been created already?

That’s not really the right question (see above). However, keep in mind that any data/metadata that has already been written to disk will not use the special vdev. It only applies to future writes.

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@user0241233

what would be the purpose of multiple metadata vdevs within a single pool?

More capacity for the special blocks? Balanced reads/writes?

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@user0241233

With the addition of a new vdev, I’d also be looking to add a metadata vdev as well.

Please have an understanding of what you’re getting into. A special vdev is as important as a data vdev. If it fails or you lose it? You lose your entire pool.

Please use caution, and don’t think you need something just because it sounds useful.

EDIT: This is not hypberbole. You can find examples (in the old forums) of users losing their entire pool because they played around with a Dedup vdev or special metadata vdev.