No QCOW2 on ZFS?

drdownload

Member
Sep 7, 2017
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If I store an VM Image on an ZFS storage I only get RAW as option for image format.

I assume it's because ZFS supports thin provisioning.
 

wolfgang

Proxmox Staff Member
Staff member
Oct 1, 2014
5,131
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No,
with zfs pool plugin you use zvols what is the bock device emulation.
So you have a raw device in qemu.
 

wolfgang

Proxmox Staff Member
Staff member
Oct 1, 2014
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If you want QCOW2 you need to add the storage as "Folder".
Never do this because qcow is cow and zfs also.
A cow fs on a cow fs will kill the performance and bring no benefit or features.
 
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Nemesiz

Active Member
Jan 16, 2009
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Maybe someone use qcow2 on zfs because of personal reasons like temporary or migration between different storage formats.
 

tom

Proxmox Staff Member
Staff member
Aug 29, 2006
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Maybe someone use qcow2 on zfs because of personal reasons like temporary or migration between different storage formats.
As long as you ZFS as a directory storage, then you can store any file, also qcow2 files. But this is NOT recommended, see above.
 

LnxBil

Famous Member
Feb 21, 2015
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Germany
bring no benefit or features.
Oh yes it does have benefits! Yes, plural!
* you can jump in between snapshots without cloning
* create snapshot trees
Both is unavailable in ZFS, so using cow2 on a zfs-based directory (if you only have ZFS available) is the only way to achieve this.

I use it quite often and never experienced any bottlenecks, yet I know that COW-on-COW has its drawbacks, but the benefits outweigh the drawbacks in my case.
 

drdownload

Member
Sep 7, 2017
38
1
13
38
I never thought about drawbacks of cow on cow to be honest. Thanks for the clearification!.

Since I only use proxmox with my homelab (at work we use VMware) I maybe switch to ext4 for my proxmox drives.
 

fireon

Famous Member
Oct 25, 2010
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iteas.at
maybe switch to ext4 for my proxmox drives.
Yes, do that :) Storage is depending on features that you need for. For Migrations, copy and testing qcow2 on ext4 is the easiest way.

But for all other things in productive environments with no HW-Raid ZFS or Ceph are real the best :)
With HW-Raid use LVM-Thin.
 

fcymk2

New Member
Sep 7, 2019
13
0
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35
Never do this because qcow is cow and zfs also.
A cow fs on a cow fs will kill the performance and bring no benefit or features.
If use directory and raw format? Are there any disadvantages to this?

Sometimes need to copy the disk to another machine.
 

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