Your cmdline looks strange: it does not match a usual Proxmox host (no amd_iommu=on and no initrd=) and it implies LVM instead of ZFS. Please run
Memory could be an issue if ZFS uses 50% and the other VM uses 25% (because all memory must be pinned) then allocating 25% could be a problem (in ZFS does not release memory quickly enough). This is easily tested by temporarily reducing the memory amount (a lot), and I would expect memory allocation errors in the logs.
Note that KSM won't apply to VMs that use PCI passthrough (because of Direct Memory Access as I said before).
EDIT: Timeouts during starting of VMs used to be a sign to taking to long to allocate and map large amounts of pages into actual memory, but I thought that was fixed long ago.
cat /proc/cmdline on the Proxmox host.Memory could be an issue if ZFS uses 50% and the other VM uses 25% (because all memory must be pinned) then allocating 25% could be a problem (in ZFS does not release memory quickly enough). This is easily tested by temporarily reducing the memory amount (a lot), and I would expect memory allocation errors in the logs.
Note that KSM won't apply to VMs that use PCI passthrough (because of Direct Memory Access as I said before).
EDIT: Timeouts during starting of VMs used to be a sign to taking to long to allocate and map large amounts of pages into actual memory, but I thought that was fixed long ago.
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