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Maxing out Array - ZFS Pool Questions (types and spin-up)

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Hi!

I'm running almost at capacity with the array, in the sense of amount of disks. Right now I'm at 22 disks totaling 320TB plus one parity drive (I know, but I've never had a failure)...

I could start to upgrade the disks, but doing the math I could start migrating to 28TB drives, or moving 8TB to 20TB, but cost of moving to 28TB would be around 8-10K euros, less than ideal.

While I understand that dual or larger arrays doesn't seem to be coming in the near-term future, ZFS pools seems the path forward, specially also since a pool can have 200 disks.

But I have some questions:

  • Can a ZFS pool (or any pool) spin up only the disk being read/written to?

  • Which type of ZFS pool is best used for large amounts of disks?

My initla tests using trial seems to spin up all the disks, but if I read TrueNAS' documentation they only spin up the disk in use.

Solved by JorgeB

  • Community Expert
  • Solution
34 minutes ago, PeterDB said:

While I understand that dual or larger arrays doesn't seem to be coming in the near-term future

Multiple array support is expected soonish, but it may be some months, or more.

35 minutes ago, PeterDB said:

Can a ZFS pool (or any pool) spin up only the disk being read/written to?

ZFS pools stripe the data betwwen all pool menber, any riete (or read) will spin upo all the devices.

35 minutes ago, PeterDB said:

Which type of ZFS pool is best used for large amounts of disks?

Typically RAIDZ2 for large disks, but also keep in mind the vdev width, e.g., general recommendation is up to twelve drives for RAIDZ2, you can use a little more if IOPS are not critical, more than that, you should use another vdev, e.g., a 30 drive wide RAIDZ2 pool is not typically a good idea, though I do have a few pools that are 24 wide, and work fine, but at a certain point, too-wide pools will become slow, especially with resilvering and scrubs.

  • Author

Thanks @JorgeB this good info.

  • 4 weeks later...
  • Author
On 12/7/2025 at 10:16 AM, JorgeB said:

Multiple array support is expected soonish, but it may be some months, or more.

Just read the latest newsletter and it's officially mentioned that the What's coming in 2026 section:

Multiple Arrays

Expanded storage configuration capabilities to support more advanced and diverse use cases.

Yay..

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