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Something wrong with ZFS expansion? Incorrect useable space.

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image.png

I have 3x10TB drives. I started as raidz1 with 2 disks, 10TB useable, which is correct. Once I expanded with another 10TB, only got ~5TB added of useable space.

Raidz1 with 3x10TB should have 20TB useable space.

It's scrubbing right now, I think it does that automatically after an expansion.

  • Community Expert
10 minutes ago, veganbtw said:

Once I expanded with another 10TB, only got ~5TB added of useable space.

Where do you see that? 14.3T mentioned there is the raw storage that's currently in use, not the total available size.

Edited by Kilrah

  • Author

It's also on the main screen:

image.png

  • Author
19 minutes ago, Kilrah said:

Yeah, after doing some more reading, seems to be using the same parity-to-space ratio as the original configuration and a re-writing of all data is required to fix it, might as well re-create the whole pool. 🤦‍♂️

Why even release a feature that doesn't even work properly. Would've preferred to not even be aware of this 'feature' altogether.

Hi all,

I understand that after a vdev expansion, old blocks keep the old data-to-parity ratio and only newly written data uses the new ratio, so usable space stays lower until data is rewritten.

What I’m looking for is a tool or reliable method to detect which blocks/data in the pool have already been rewritten using the new data-to-parity ratio vs which are still using the old layout. Ideally it would let me:

  • detect or list files/blocks that are already rewritten

  • distinguish them from those still using the old parity scheme

I am aware of this tool: https://github.com/markusressel/zfs-inplace-rebalancing but as far as I can tell it just rewrites files and doesn’t actually check which blocks are already using the new ratio.

Also, does anyone know if zfs rewrite can be used for this purpose?

Thanks!

Edited by skler

  • Community Expert

There's no solution at the time, zfs rewrite will help to recover some space, since it will rewrite the data with the new data to parity ratios, but the stats will still be reported using the old one.

A real fix will need to be made upstream by OpenZFS.

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