[SOLVED] VM Harddrive passthrough: VM and host are not in sync

[maeries]

it may be a bad title, but I don't know how else to describe it.

So I have a Ubuntu Server VM on Proxmox and I want to passthrough some drives (as passing through a directory does nto work afaik). I used

sudo qm set 105 -scsi2 /dev/sdb1

to do so. I then mounted it in the guest by putting

/dev/sdb        /mnt/festplatte1        ext4    defaults        0       0

info the fstab and running mount -a. The drive is also mounted on the host.

Now to the part i dont understand. If I create a folder on that drive in the VM, it also appears on the host, but it takes a minute. Is it normal, that it takes so long? And when the host created a folder on that drives it only appears on the host, not on the VM. Why is that? And last, but not least: If the host deleted the folder created by the VM it disappears for the host, but reappears some time later. Also for the VM the folder never disappears.

Is all that behaviour normal? What I want is basically a container bind mount, but for VMs

 

[leesteken]

The drive is also mounted on the host.

This is the problem. Most filesystems assume that the drive is not shared between different machines (virtual or physical) at the same time, as most (physical) drives are not designed to be connected to more than one controller/machine (at the same time). They cache information assuming that no one will change the data on the drive behind their backs. Use SMB or NFS is you want to share folders between machines (virtual or otherwise).

Is all that behaviour normal? What I want is basically a container bind mount, but for VMs

EDIT: Look into QEMU 9p or virtio-fs to share a host folder via a virtual PCI devices. Or use SPICE folder sharing via WebDAV.

 

[Dunuin]

Also check your data integrity. You probably already corrupted some data by mounting it in parallel on two OSs.

 

[maeries]

This is the problem. Most filesystems assume that the drive is not shared between different machines (virtual or physical) at the same time, as most (physical) drives are not designed to be connected to more than one controller/machine (at the same time).

That was also my first guess, but since none of the like five tutorials I read mentions it, I tought it is fine

EDIT: Look into QEMU 9p or virtio-fs to share a host folder via a virtual PCI devices. Or use SPICE folder sharing via WebDAV.

Do you mean running sudo qm set 105 -virtio2 /dev/sdb1 or are you talking abount something different?

 

[maeries]

Also check your data integrity. You probably already corrupted some data by mounting it in parallel on two OSs.

yeah, just ran fsck on the drive

 

[Dunuin]

yeah, just ran fsck on the drive

That might be a good indicator, but it can't tell you if your actual data got corrupted. Without a checksumming filesystem like ZFS you would need to compare file checksums against the file checksums of a known good backup.

Do you mean running sudo qm set 105 -virtio2 /dev/sdb1 or are you talking abount something different?

Completely different.