You can't extend the existing raidz1 vdev by adding another disk but you can add another vdev to the pool to increase the pool's capacity. You'll need more than one additional disk if you want to retain redundancy. For example, you could use two disks to add a mirror vdev or 3+ disks for another raidz1 vdev.
Answer from Mike Fitzpatrick on Stack ExchangeProxmox
forum.proxmox.com › home › forums › proxmox virtual environment › proxmox ve: installation and configuration
[SOLVED] - Adding more disks to an already exist ZFS RaidZ1 | Proxmox Support Forum
May 4, 2021 - Since you already have a raidz1, you would add another raidz1 with zpool add hddpool raidz1 /dev/disk/by-id/... ... @ph0x Thank you so much for your reply, would it be possible to tell me where did you get this command? because I searched for ...
DiskInternals
diskinternals.com › home › raid recovery › zfs raid expansion: how to expand raidz and zfs pools safely
ZFS RAID Expansion: How to Expand RAIDZ and ZFS Pools Safely | DiskInternals
1 week ago - However, in ZFS, the RAIDZ structure is more fixed, and expanding it requires either adding a new vdev (a collection of disks) to the pool or replacing each disk with larger ones, which can be time-consuming and limits flexibility.
debian - expanding ZFS raid-z vdev with newly added disks? - Unix & Linux Stack Exchange
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TrueNAS Tutorial: Expanding Your ZFS RAIDz VDEV with a Single Drive [YouTube Release] - Youtube Releases - Lawrence Systems Forums
Additional Resources: My Previos Video on TrueNAS: How To Expand A ZFS Pool TrueNAS Scale 24.10 Documentation Managing Pools | TrueNAS Documentation Hub ZFS In Place Rebalanci… More on forums.lawrencesystems.com
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September 13, 2024Expanding RAIDZ1
Hello All, I recently set up a RAIDZ1 for home storage. I originally ordered 4 18 TB HDD (Seagate Exos drives), but one of them was faulty out of the box. It took almost 8 months of fighting with the distributor to get it replaced, but I just couldnt… More on forum.openmediavault.org
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December 4, 2025Adding Disk to RaidZ1
Hi, i use Version: TrueNAS-13.0-U5.2 with 3x6tb drives in the pool, i reached 80%+ space usage and wanted to add another 6tb drive but i can't figure out how i should be able to. if i want to add another vdev core tells me i need at least 3 disks... "This type of VDEV requires at least 3... More on truenas.com
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July 25, 2023GitHub
github.com › openzfs › zfs › discussions › 15232
RAIDZ Expansion feature discussion · openzfs/zfs · Discussion #15232
No. A mirror vdev is not raidz-1. But this is what you can do: Break the mirror, remove one drive. Take that drive, a second fresh one, and a sparse file, and make your raidz1 in a new pool, not the same pool!
Author: openzfs
Top answer 1 of 2
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You can't extend the existing raidz1 vdev by adding another disk but you can add another vdev to the pool to increase the pool's capacity. You'll need more than one additional disk if you want to retain redundancy. For example, you could use two disks to add a mirror vdev or 3+ disks for another raidz1 vdev.
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I know this question is old, but I just came across it. It looks like the ability to extend a RAIDZ one drive at a time is in the works! No ETA that I've seen though.
https://www.freebsdfoundation.org/blog/openzfs-raid-z-online-expansion-project-announcement/
Lawrence Systems
forums.lawrencesystems.com › youtube releases
TrueNAS Tutorial: Expanding Your ZFS RAIDz VDEV with a Single Drive [YouTube Release] - Youtube Releases - Lawrence Systems Forums
September 13, 2024 - Additional Resources: My Previos Video on TrueNAS: How To Expand A ZFS Pool TrueNAS Scale 24.10 Documentation Managing Pools | TrueNAS Documentation Hub ZFS In Place Rebalancing Script FreeBSD Developer Summit: Raid-Z Expansion video https://youtu.be/yF2KgQGmUic?si=9qk66NC_xF8BIKWQ Connect With Us Hire Us for a project: Hire Us – Lawrence Systems Toms’ Twitter 🐦 https://twitter.com/TomLawrenceTech Our Website https://www.lawrencesystems.com/ ...
openmediavault
forum.openmediavault.org › index.php
Expanding RAIDZ1 - General - openmediavault
December 4, 2025 - I expanded my vdev with zpool attach <poolname> <raidz vdev name> <new device name>. There was an expansion step, took around 12 hours, then resilvering another 8. The pool remained usable although noticeably slower during this.
TrueNAS Community
truenas.com › forums › truenas core › hardware and upgrades
Adding Disk to RaidZ1 | TrueNAS Community
July 25, 2023 - "This type of VDEV requires at least 3 disks" "Caution: Adding data vdevs with different numbers of disks is not recommended. First vdev has 3 disks, new vdev has 1." i just want to add more space ... At present, you can NOT add a column / disk to a RAID-Zx vDev. It is a limitation of ZFS. Their are 2 ways to expand a pool:
FreeBSD Foundation
freebsdfoundation.org › home › blog › openzfs raid-z expansion: a new era in storage flexibility
OpenZFS RAID-Z Expansion: A New Era in Storage Flexibility | FreeBSD Foundation
February 24, 2025 - Better Resource Utilization: Previously, expanding RAID-Z required adding an entirely new vdev, often leading to inefficient use of older pools. Now, storage scales dynamically. Minimal Downtime: Expansion occurs while the system remains operational. This demonstration of RAID-Z expansion uses a recent FreeBSD 15-CURRENT snapshot: bsd_FreeBSD-15.0-CURRENT-amd64-zfs-20250116-054c5ddf587a-274800.raw from 2025/01/16, which includes all the latest OpenZFS 2.3 goodies.
TrueNAS Community
truenas.com › forums › truenas scale › hardware and upgrades
Adding a drive to a RAIDZ1 pool | TrueNAS Community
August 9, 2023 - Click to expand... You DON'T want to do that !!!!!!!! You would extend the pool with an additional vdev. But that vdev would be only the new single drive. So it has zero redundancy. If that new drive fails, your pool is gone. And new drives fail with a much higher probability than those that ...
Reddit
reddit.com › r/proxmox › add third drive to a zfs mirror possible?
r/Proxmox on Reddit: Add third drive to a zfs mirror possible?
November 26, 2024 -
Hi, i have a zfs mirror of 4TB drives and i want to add a third 4TB drive. Is it possible to turn zfs mirror to raid z1 without loosing my data?
Update:
so i know i cant turn a mirror to a z1 but how hard is it to add drives to raid z1? for example from 3 to 4
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You can break the mirror and remove one of the drives, then use that and the third drive to create a raidz1 in a degraded state (one drive missing). Now copy the files from the degraded mirror to the degraded raidz1, wipe the mirror, and add it to the raidz1.
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To a raidz1? No. To a three drive mirror? Yes.
Ars Technica
arstechnica.com › gadgets › 2021 › 06 › raidz-expansion-code-lands-in-openzfs-master
ZFS fans, rejoice—RAIDz expansion will be a thing very soon - Ars Technica
June 15, 2021 - Credit: Matthew Ahrens · From a practical perspective, Ahrens’ new vdev expansion feature merely adds new capabilities to an existing command, namely, zpool attach, which is normally used to add a disk to a single-disk vdev (turning it into ...
Proxmox
forum.proxmox.com › home › forums › proxmox virtual environment › proxmox ve: installation and configuration
Adding new disks to Raidz | Proxmox Support Forum
March 8, 2022 - Then you should look at the zpool attach command as the zpool add command will create an additional vdev and what you want IIUC is ... NAME STATE READ WRITE CKSUM fastsas5 ONLINE 0 0 0 raidz1-0 ONLINE 0 0 0 scsi-35001e82002774394 ONLINE 0 0 ...
Reddit
reddit.com › r/zfs › raid-z expansion
r/zfs on Reddit: raid-z expansion
August 27, 2022 -
I have four disks three of which are configured in raidz1-0. I'd like to expand my raidz using the fourth disk but it throws an error message I cannot figure out how to address. I run the following command zpool attach testpool raidz1-0 /Dev/sda It states "cannot attach /Dev/sda: can only attach to mirrors and top level disks ". I run Ubuntu 22.04 and freeBSD 13.1 but both behave in a similar fashion. Someone guide me how to successfully perform a raidz expansion. Thanks
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Raidz expansion isn't added to open zfs yet
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You're Doing It Wrong. Read the man pages. If you want a 4-disk raidz1, BACKUP 1ST. Then destroy the pool and rebuild it as a 4-disk raidz1. ' zpool create -o ashift=12 -o autoexpand=on -O atime=off $poolname raidz /dev/disk/by-id/ ' and use those device names. Worst case you might have to do a zpool labelclear to re-use the disks. Then restore from backups to the new pool. The most common error people tend to make is doing a ' zpool add ' where they shouldn't. You however are trying to attach a mirror disk to a raidz, and ZFS is rightfully telling you A) it can't do that, and B) to educate yourself before proceeding further. Finally, you're using a capital D where it should be /dev
Unraid
forums.unraid.net › home › unraid os support › general support › expanding raidz pool by adding single disk
Expanding Raidz pool by adding single disk - General Support - Unraid
December 31, 2024 - I have a zpool of 3x2TB NVME drives. I would like to add a fourth. They are all the same drive from the same manufacturer. I'm trying to use zfs attach and getting an error of cannot attach nvme-eui.6479a78dd00000d8 to raidz1-0: can only attach to mirrors and top-level disks I've tried doing it f...
TrueNAS Community
truenas.com › forums › archives › freenas (legacy software releases) › freenas help & support › storage
Expanding a RAIDZ with a set of different sized drives. | TrueNAS Community
October 27, 2017 - Click to expand... It's a per vdev property. If your vdevs are raidz1, you can loose one disk per vdev. If both are from the same vdev this vdev become unavailable and so the pool, and the data is gone. (ZFS stripes data over vdevs, that means that pieces of data are spread over each vdev.
Reddit
reddit.com › r/zfs › noob question - how to expand zfs in the future?
r/zfs on Reddit: Noob question - how to expand ZFS in the future?
February 11, 2025 -
I have two 6tb drives to be used as a media server, and I would like to be able to expand the storage in the future. If I wanted them in a mirror as one vdev, would I then be able to add another two 6tb drives as a mirror vdev to the pool to have 12tb of usable storage? Should I instead have each drive be it's own vdev? Can I create a stripe of my two vdevs now, and later add a drive for redundancy?
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Yes. Depends on your risk tolerance. No.
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I don’t know that what I have to offer is helpful to you or not, but I’ll give my recent experience. I started with 1 vdev 4x12tb raidz1. It filled up so I just added a second matching vdev. Now I have 2xvdev 4x12tb raidz1 each. As long as I only have 1 drive per vdev fail at a time before rebuilding it’ll be faster and still recoverable. I deleted a good chunk of my downloaded data and redownloaded it so it would rebalance across both vdevs. Having 2x vdev 4x12tb raidz1 also allows for better IOPS than I’d I started over with 8x12tb raidz2 I also have an extra drive that is a backup in case one fails that I copied important stuff to during the process. I hope this helps
TrueNAS Community
truenas.com › forums › archives › freenas (legacy software releases) › freenas help & support › storage
Expanding RaidZ1 with single disk | TrueNAS Community
August 10, 2018 - Click to expand... With traditional mirrors (2 disks per vdev) that's correct. That's why I said that a ZFS mirror isn't limited to 2 disks. Depending on your risk tolerance one might look at 3 or 4 way mirrors.
OneUptime
oneuptime.com › home › blog › how to expand a zfs pool by adding new disks on ubuntu
How to Expand a ZFS Pool by Adding New Disks on Ubuntu
March 2, 2026 - If your pool is a mirror, you can replace disks one at a time with larger ones and then expand the vdev's usable size once all members are replaced. Starting pool: mirror of two 1TB disks, replace with 2TB disks.
Reddit
reddit.com › r/zfs › how easy to add more disks later on?
How easy to add more disks later on? : r/zfs
January 10, 2024 - If I’m not mistaken there is a restriction that if you start with raidz(x) you can not expand another vdev with raidz(y) within the same pool so unless you’re planning your expansion to add another 12 drives in raidz3 you are essentially stuck with your original pool capacity. With the coming release 2.3 in a year or so you will be able to directly expand the size a RAID-Z with additional disks. More replies ... For a "movie" storage I recommend you take a look about SnapRaid, zfs is for some serious stuff that if you mess up you lose everything that require rebuild from backup, if you dont have backup plan, think twice about using a massive zpool for you precious data.