VirtIO SCSI single stuck to 14 hard disks

[CS35]

Hello everyone,

we are running a Proxmox 5.2-10 and are attempting to attach around 30 disks to a VM using SCSI device.
According to the documentation, section hard disk, if you set VirtIO SCSI single as the default SCSI controller you get "no limit" since Qemu will create a new controller for each disk, instead of adding all disks to the same controller. So we tried that and actually it's the same in the interface, after 14 hard disks we can't add more SCSI device we have to fall back to IDE, VirtIO Block etc ...
Has anyone already succeeded with this ?

 

[wolfgang]

Hi,

you still on the SCSI bus what has 14 disk limit at PVE
Nowhere the docu is noted that if you use Vitrio single you can create as many disks you like.

If you aim at maximum performance, you can select a SCSI controller of type VirtIO SCSI single which will allow you to select the IO Thread option. When selecting VirtIO SCSI single Qemu will create a new controller for each disk, instead of adding all disks to the same controller.

 

[dcsapak]

even if we create a controller per disk, there is still a hard limit (atm) for 14 scsi config entries

 

[Ulrar]

That's unfortunate, that's really the only idea we had on how to allow for easy decrease in disk space for a particular machine : Just have one disk per website, and when you want to delete a website just delete the associated disk, freeing up the space to be allocated elsewhere without having to go through the dangerous disk shrinking procedure.
Oh well, thanks for the answer

 

[CS35]

Thanks for your fast answers.
True it's me who understood that there would be no limit, the doc indeed didn't state that but I thought it would, or at least more than 14 hard disks.
I'm hoping the hard limit will be raised.
Thanks again.

 

[Andrew Hart]

You could still do this:
Create disks in a binary chop manner...(exponential might be a better name)..i.e. disk1 10GB, disk2 20GB, disk3 40GB,
Then inside the VM add the disks to a VG, Then create LVs for your websites. If you need to recover disk space you can pv move the data off the disk in question to recover the disk amount you need.

 

[Ulrar]

That's the backup idea yes, more or a less : put everything in an LVM volume and if needed create a new smaller disk, use pvmove and delete the old disk. That'll do !

 

[spirit]

About virtio-scsi-single, the limit is the number of virtual pci slot , that's why it's limited in number.

But it could be possible, for classic virtio-scsi controller, to use 256 disks. currently, only 7 disks are assigned by controller. (to match older scsi controller). So 512 disks with 2 controllers, instead 14.