Re: Upsizing a ZFS filesystem - shift question

From: Alan Somers <>
Date: Thu, 27 May 2021 12:36:28 -0600
ashift affects how the data is laid out on disk, so you can't change it
after the drives have been replaced.  And you don't want to use ashift=9
for the new drives; their performance will suck.  Your best bet is to
create a new zpool, then send | receive the data from the old pool.

On Thu, May 27, 2021 at 12:33 PM joe mcguckin <> wrote:

> I have an existing 32TB filesystem (2 X 8T vdevs). I want to upgrade each
> of the drives to 16TB. I pulled one drive and tried a ‘zfs replace’ comand,
> but zfs replied with some message about new drive
> optimal ashift doesn’t match the vdev. It suggested Retrying  the
> ‘replace’ command with ‘zfs replace -o ashift=N’
> Ok, a little investigation shows the existing filesystem has an ashift of
> 9. These are older 2T drives with 512 byte sectors. The newer drives are
> 4kn sectors.
> Is ashift settable on a drive by drive basis? Can I temporarily set ashift
> on a drive until all the drives in a vdev have been replaced?  Once all
> drives have been replaced, how do I set ashift=12 for all the drives in the
> vdev?
> After replacing all the drives, will the additional space magicially
> appear or is there an additional command or series of steps?
> Thanks,
> Joe
> Joe McGuckin
> ViaNet Communications
> 650-207-0372 cell
> 650-213-1302 office
> 650-969-2124 fax
Received on Thu May 27 2021 - 18:36:28 UTC

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