On Tue, Sep 08, 2020 at 02:38:17PM +0200, Peter Krempa wrote: > On Tue, Sep 08, 2020 at 08:19:21 -0400, Alexander Wels wrote: > > Hi, > > > > I am working on a project, and one of the requirements is that I can > > hotplug a large number of disks. Think several dozens to potentially 100+. > > The guest OS will be some linux flavor so it should have no problem with a > > large number of disks. > > > > During my experimentation I quickly ran into the "No available PCI slots" > > limit. I found https://libvirt.org/pci-hotplug.html explaining to me why > > the limit is there. Now I could add a bunch of pcie-root-ports ahead of > > time, but there is likely a limit to that as well. So before I go down some > > crazy paths, I figured I would ask on here if there is a better plan than > > adding a bunch of root ports for adding a large number of hotplugged disks? > > I strongly suggest using a virtio-scsi controller and plugging disks > into it. You can have a fairly large number of LUNs per controller, so > that will severely decrease the amount of required PCI slots. You can > obviously add more controllers if you need even more LUNs. A single virtio-scsi controller can support ~4 million LUNs. IOW you'll face a wall of other problems before you get anywhere near needing a second virtio-scsi controller due to LUN exhaustion :-) Only real reason for multiple virtio-scsi controllers that I see is if you want to setup different host CPU affinity for each controller for I/O thread performance tuning Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|