What does it mean to mark storage as shared

[jhm]

Looking at the documentation at https://pve.proxmox.com/wiki/Storage, it says under "Common storage properties" that the property "Shared" marks the storage as shared. I could have guessed that without the documentation. But it doesn't explain what this means. Is this the same meaning of shared as is used in the table at the top of the page? Then why is it possible to set this manually? I would expect it to be a property that is implied by the type of storage.

My guess would be that if you mount some kind of network storage manually, so without using the Storage mechanism of Proxmox, and then add this to Proxmox as a directory storage, that you can mark it here as being shared storage. Is this indeed the point of this property? If so, it would be nice if this is explained in the documentation. I would also be interested to know what Proxmox uses this information for.

 

[bbgeek17]

Looking at the documentation at https://pve.proxmox.com/wiki/Storage, it says under "Common storage properties" that the property "Shared" marks the storage as shared. I could have guessed that without the documentation. But it doesn't explain what this means. Is this the same meaning of shared as is used in the table at the top of the page? Then why is it possible to set this manually? I would expect it to be a property that is implied by the type of storage.

You can have an iSCSI LUN0 attached to node A, a LUN1 attached to node B, and LUN2 to node C. The storage in this case is of type "iSCSI", it could be "shared", but in this particular example its not. Marking it "shared" would be wrong.

If you attach LUN0-2 to all nodes (A,B,C) simultaneously - the storage is now "shared". You, as the administrator, have to tell PVE that storage is "shared" and it should be treated as such.

At Blockbridge we take a different approach. Under normal operational conditions an iSCSI or NVMe/TCP LUN is attached to NodeA. This LUN is a one to one match for a VM Image (disk). When the VM is live-migrated, the LUN is "magically" attached to the target node with the help of the storage plugin. To inform PVE that this is possible we need to mark the storage "shared".

As you can see there is a lot of flexibility in PVE storage handling, but with that comes some complexity. Hopefully this helps you orient in storage world a bit better.

Cheers,

---

Blockbridge : Ultra low latency all-NVME shared storage for Proxmox - https://www.blockbridge.com/proxmox

 

[fiona]

Hi,

Looking at the documentation at https://pve.proxmox.com/wiki/Storage, it says under "Common storage properties" that the property "Shared" marks the storage as shared. I could have guessed that without the documentation. But it doesn't explain what this means. Is this the same meaning of shared as is used in the table at the top of the page? Then why is it possible to set this manually? I would expect it to be a property that is implied by the type of storage.

it can be inferred for some storage types like NFS, PBS (always shared, but you can still restrict it to certain nodes). But it cannot be inferred for a directory or LVM storage for example, because they could be both.

My guess would be that if you mount some kind of network storage manually, so without using the Storage mechanism of Proxmox, and then add this to Proxmox as a directory storage, that you can mark it here as being shared storage. Is this indeed the point of this property? If so, it would be nice if this is explained in the documentation. I would also be interested to know what Proxmox uses this information for.

Yes, exactly.

EDIT: also sent a patch: https://lists.proxmox.com/pipermail/pve-devel/2023-October/059318.html