Real thin provisioning with CEPH

Nov 8, 2017
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Muscat
Hi guys
We have Proxmox and Ceph as our storage.
I understand that by turning on discard on the VMs and doing fstrim we can reclaim the unused storage.
But my question is why as soon as I create a VM with E.G 200GB storage from CEPH pool, Proxmox will deduct that 200GB from the CEPH POOL.
Even after discard and fstrim if the storage decrease to let's say 30GB, but there is no way I can use that 200GB to provision another VM.
My purpose to achive this is to somehow oversell the storage with caution.
I have attached a screenshot of my CEPH Pool.
 

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Alwin

Proxmox Retired Staff
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Aug 1, 2017
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The storage shows the configured size, not the actual one. You can check with rbd du <pool>/<disk-name> the used size.
 
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Nov 8, 2017
99
3
13
31
Muscat
The storage shows the configured size, not the actual one. You can check with rbd du <pool>/<disk-name> the used size.
I know I can see the actual size using those commands, but the issue is my storage in Proxmox will reduce by the given size, not the actual size.
For example, I have a 1TB Pool and storage of CEPH (RDB) in Proxmox, once I create an empty VM with a 100GB virtual disk, my storage has 900GB left and usable for other VMs.
 

Alwin

Proxmox Retired Staff
Retired Staff
Aug 1, 2017
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Proxmox VE doesn't impose a limit on the storage, it is just statistics.
 

spirit

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Apr 2, 2010
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www.odiso.com
I know I can see the actual size using those commands, but the issue is my storage in Proxmox will reduce by the given size, not the actual size.
For example, I have a 1TB Pool and storage of CEPH (RDB) in Proxmox, once I create an empty VM with a 100GB virtual disk, my storage has 900GB left and usable for other VMs.

This is not normal. the space is not reserved and not used until you write datas in your vm.
as proof, you can also create vm disk bigger than available storage in your pool.

Just check the storage disk usage graph, create a vm with a disk, the disk usage space of the storage shouldn't change
 

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