Mirror VDEVs: Mix, or match, different brands of drives?

TrueNAS General
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I’m setting up a new pool, with two 2-disk mirror VDEVs. I have four disks, two each of 18TB Seagate IronWolf Pro 7200’s, and of 18TB Western Digital DC HC550s (also 7200).

Should I put the same brand in the same VDEV, i.e. both Seagates in one VDEV and both WDs in the other? Or should each VDEV have one of each? I’m assuming that these are equally performant. I’ve seen advice to set up pools using disks from different batches to guard against same-batch manufacturing failures, but I don’t know how this relates to any potential benefit of sticking with the same brand, or if this even matters at all.

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It probably does not matter much.
I would personnaly mix drives to ensure that the vdevs are identical.

But actually I would not run 18 TB as 2-way mirrors: Too much data at risk in case of drive, too long time to resilver if the drive was filled. At this size, I’d want 3-way mirrors if the IOPS performance of a striped pool is required, or go raidz2 for more resiliency.

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I suggest mixing drives… I do the same with my refurbished and new drives: on paper, you have a higher chance of avoiding batch failures.

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Unless you need the performance of mirrors, I would go for RAIDZ2 because it gives you the same capacity and you can have any two disks fail without loss of data (whereas with 2x mirror if you lose both disks from a mirror at the same time, then you will).

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Mirror VDEVs are more flexible though.

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Thanks, but I prefer the flexibility of mirror VDEVs; I’m willing to take the chance of a two-same-VDEV drive failure in exchange for being able to easily add/change disks without having to get a whole bunch at once, or destroy and rebuild the whole pool.

(As @Davvo said more succinctly while I was typing this.)

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Very true.

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If you can it’s probably worth mixing the manufacturers up to avoid bad batches as long as the drives are similar (ie same size, same similar rotational speed)

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Mirrors are the best choice for a whole host of reasons, but obviously there’s a cost to losing half your storage.

Apart from having redundancy at a hardware level between two drives, it’s infinitely scalable and configurable.

As an example… if you have 2x8 TiB drives and 2x10 TiB drives?

You can have two 8TiB vdevs (1x10 and 1x8 mirrored, you get 8 TiB) for a total of 16TiB

Or you can do a VDEV 2x10 TiB and the other 2x8.

You can build a system with two drives, or scale it up to one with disk shelves and redundancy across shelves and even HBAs. Mirrors are the choice if you can afford them.

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