If the host span is tiered, all new file systems created on it are automatically tiered as well.
In this case, no file system can be created unless the span has enough space on both tiers. If you specify an initial size for a new tiered file system, the NAS server allocates the minimum possible amount of space from Tier 0 (metadata) and the rest from Tier 1 (user-data). Otherwise, it allocates the smallest possible amount from both tiers.
If you specify a confining capacity for a new tiered file system, it applies only to Tier 1 (user-data). If you need Tier 0 (metadata) to also be confined, use the filesystem-confine command to confine it manually. As user data is normally bigger than metadata, the two tiers are typically confined to different capacities.