IMHO, both. In a storage industry where the hardware cost to protect data keeps rising, ZFS represents a software solution to the problem of wobbly disks and data corruption. Thus it is a threat to hardened disk array model of very expensive engineering on the outside to protect the soft underbelly of ever-cheaper disks on the inside.

It’s Software Version of the Initiation Rite in A Man Called Horse
Before I jump into the review of ZFS, let me share what I like best about it, from a slide in the modestly titled “ZFS, The Last Word In Filesystems” presentation:

ZFS Test Methodology

  • A Product is only as good as its test suite [amen, brother!]
    • ZFS designed to run in either user or kernel context
    • Nightly “ztest” program does all of the following in parallel:
      • Read, write, create and delete files and directories
      • Create and destroy entire filesystem and storage pools
      • Turn compression on and off (while FS is active)
      • Change checksum algorithm (while FS is active)
      • Add and remove devices (while pool is active)
      • Change I/O caching and scheduling policies (while pool is active)
      • Scribble random garbage on one side of live mirror to test self-healing data
      • Force violent crashes to simulate power loss, then verify pool integrity
    • Probably more abuse in 20 seconds than you’d see in a lifetime
    • ZFS has been subjected to over a million forced, violent crashes without losing data integrity or leaking a single block

Read The Rest Of ZFS: Threat or Menace? Pt. I