Mirror SSD pool, add new mirror vdev or create a new pool with 4 SSD?

TrueNAS General
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My current system has a pool with NVMe SSD mirror for applications and hot data staging, and I recently got hands on some more parts so I have 2 more additional M.2 slots to add new SSDs. Given my relatively light usecase (~25TB written per year on a 1200TBW rating drive), here are two options I’m considering:

  1. add 2nd mirror vdev to the existing pool to expand it, without too much effort
  2. backup and destroy the existing pool and create a new raidz2 pool, then restore from backup

As I plan to add the exact same SSDs as the existing pool, I’m leaning to the 1st option as it’s easy and both options give me the same total storage. Just wondering how is the 2nd option, I lost read speed and need more efforts/downtime to migrate, but gain any 2 drives failure vs any 1 drive from each vdev. As a homelab media/backup NAS, does it worth it to go from option 1 to 2?

One thing I forgot to consider is data balancing if go with option 1 but I assume ZFS and TrueNAS will do its own magic right?

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  1. add 2nd mirror vdev to the existing pool to expand it, without too much effort

This is what I’d recommend for performance reasons.

Sort of. New data being written should balance things out. Existing data on the drives won’t be re-written, but if this for staging I suspect existing data will age out on its own.

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If you want write performance then mirrors are definitely the way to go.

ZFS does not rebalance the data that is already there, but over time more new data will be written to the new drives than the old.