Metadata by default is protected at one level higher than the protection policy of the data.  So for example, if the data is protected at 2d:1n, the metadata for that file will be 4x since a small file under that policy would be 3x.  In the case of 3d:1n, the metadata would be mirrored 5x.

If you have SSD metadata policies, then some or all of the metadata will be written to SSD insttead of the hard drives.  With GNA, the policy is meta-read so, in that case, one copy of the metadata will be in SSD and the rest on the hard drives.  With meta-write, all copies of metadata reside on SSD.

The good news in all of this is that metadata tends to be very small so the amount of disk space consumed by it tends to be small as well even with the mirroring.  But metadata is very important to maintain access to the data so it is important to protect it well.