Meta drive will not work with iscsi…I went through this doing a nfs/iscsi test. on iscsi and about 30 terminal servers my meta drive had zero data on it and I generally do 8kb and smaller. on nfs its utilized quite well.
We have done quite some testing on this due to iops related issues with the old kubernetes backend.
The MANY io actions that kubernetes fired, caused severe slowdowns on pure HDD, whereas adding a metadata vdev with small blocks enabled made if function very-close to an SSD. Even if we just limited it to 4K small-blocks.
Where Meta-data devs + Small-blocked enabled shines, is when the disk is being overloaded by small random iops. Which are very specific use cases.
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I am glad to hear that you took this plunge. Unfortunately disks are not cheap and the the overhead needed to keep your data safe makes it even more expensive. BUT, not as expensive as losing decades worth of data!!
The bad news - a pool made with 16TB drives should really be Z2. That said Z1 gives you a vast amount more security than striped, allowing ZFS to fix not only an entire drive failure but also individual files that suffer from bitrot or occasional sector failures. Z2 only adds protection you if you get problems with a second drive at the same time - which will hopefully not happen.