pNFS Flexible File Layout (Flex Files) is a type of layout that pNFS supports client-side mirroring.1
There is a post on reddit2 that describes the benefits of pNFS from NFS v4.2 with Flex Files. For posterity:
cbg523 via r/hpc
Actually, there are multiple fundamental differences between pNFSv4.1 from 2011 and the introduction of pNFSv4.2 with Flex Files in 2019. With v4.2 it solves the innate chattiness of the NFS protocol, adds intelligence into the client, etc. The recent addition of localio in v6.12 of the Linux kernel adds even more efficiency, bypassing the NFS protocol within the kernel when storage is local within the server, such as NVMe that is included in DGX servers.
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The advantage of course is that the client is already included in standard Linux distributions.
I think Hammerspace led the development of this, and it sounds like it addresses many of the issues of the original pNFS. This happened after I left the storage world though.