Questions about Proxmox VE SAN Integration Services

[RoxyProxy]

Hello,

I'm currently testing the Proxmox VE SAN Integration Plugin with Proxmox VE 8.4 and an IBM Storage thats directly connected via FibreChannel and I have configured multipathing. It works quite well so far.

I do have some questions though:

1. Thin-Provisioning.
Thin- Provisioning seems to work when I create a snapshot or when I expand a vmdisk afterwards. I can see that the snapshot is only taking below 25GB for a VM with a 90GB disk and 8GB of ram. And when expanding a disk, I can see on the storage that the size of the disk changes, but the usage % of the storage doesn't change, as expected.

But when creating a new VM, and it really only happens when creating a VM and not when adding a new disk afterwards, it does allocate all the space of the disk instantly.

So on a 4TB Storage, creating a VM with a 2TB disk, instantly allocates 50% of the storage (as if it was thick provisioned) , but creating a VM with a 100GB disk and then resizing it to 2TB does not instantly take 50%.
When creating a VM with no disk, and then manually adding a 2TB Disk it also instantly takes 50%.

Its not just a visual bug either, when then trying to create a VM with another 2 TB disk for example I get the error:

creating vm-104-disk-0 (size 2097152000K) from storeid swlun, vg swvg
Thin pool volume with chunk size 64.00 KiB can address at most <15.88 TiB of data.
TASK ERROR: unable to create VM 104 - creation of thin pool 'lvmth-104' in swvg error: Volume group "swvg" has insufficient free space (398143 extents): 512000 required

It seems a workaround would be creating a small disk at first and then resizing to the desired capacity, but it feels like this isn't expected behavior of thin-provisioning?

Some insight on this would be great!

2. How is the thin-provisioning and snapshot support on a shared SAN achieved?
Meaning, how does the plugin work in the background?

It would be nice to have some explanation of how its working as I couldnt find much of anything about it online.

3. Even though it seems to work and seems stable so far, I'm quite often getting the message " unsupported storage of vg 'swvg' "
Is this expected behavior of proxmox? Im guessing it is just because the starlvm isn't an officially supported storage by Proxmox VE, but it would still be nice to know if this is the case or if I did something wrong.

Thanks in advance!

[yaroslav (staff)]

Welcome to StarWind Forum.
StarWind Plugin was not tested with other shared storage providers (especially FC ones). Theoretically, it should work, but there might be some pitfalls. That might explain 3.
It is not real thin provisioning. From what I see in other systems, the plugin tricks Proxmox into thinking it is one, yet it is not for real. I hope this covers 1 and 2.

[RoxyProxy]

Hello Yaroslav, thank you for your fast answer!

Could you elaborate a bit on what you mean with it is not real thin-provisioning?
Is there a ressource where one can read a bit more about how this actually works?

Because on the website advertising this Integration, it isn't mentioned how it works or that it isn't actual thin provisioning.

Also, lets say it was used together with Starwind VSAN for Proxmox, is it then "real" thin-provisioning?

Is there a danger that when over-provisioning that data of different disks might overwrite each other?

I'll be honest, this leaves me with even more questions.

[yaroslav (staff)]

Honestly, I'd go with Proxmox 8.4+starlvm. I would see it as "snapshot and backup-ready" thick LVM. Not thin.
The volume does not behave as a true thin-provisioned one. It is not thin, it is likely thick underneath.
From what I pieced together, the plugin was the "workaround" for Proxmox users who wanted snapshots on the shared storage (e.g., integration with Veeam) in Proxmox8. With Proxmox9, there were some issues with snapshots and rolling back (there are some threads here); that's why we don't use the plugin with that version.
Now back to your questions.

Also, let's say it was used together with Starwind VSAN for Proxmox, is it then "real" thin-provisioning?

Nope, you can't do a real thin LVM, even with VSAN.
I am afraid there's no info in public access about the starlvm plugin.

Is there a danger that when over-provisioning, the data of different disks might overwrite each other?

No, I don't think so; I doubt you can over-provision that volume, causing data corruption.