On Wed, Jun 12, 2019 at 02:59:31PM +0300, Sam Eiderman wrote: > v1: > > Non-standard logical geometries break under QEMU. > > A virtual disk which contains an operating system which depends on > logical geometries (consistent values being reported from BIOS INT13 > AH=08) will most likely break under QEMU/SeaBIOS if it has non-standard > logical geometries - for example 56 SPT (sectors per track). > No matter what QEMU will guess - SeaBIOS, for large enough disks - will > use LBA translation, which will report 63 SPT instead.
--verbose please. As far I know seabios switches to LBA mode when the disk is simply too big for LCHS addressing. So I fail to see which problem is solved by this. If your guest needs LCHS, why do you assign a disk which can't be fully accessed using LCHS addressing? > In addition we can not enforce SeaBIOS to rely on phyiscal geometries at > all. A virtio-blk-pci virtual disk with 255 phyiscal heads can not > report more than 16 physical heads when moved to an IDE controller, the > ATA spec allows a maximum of 16 heads - this is an artifact of > virtualization. Well, not really. Moving disks from one controller to another when the OS depends on LHCS addressing never is a good idea. That already caused problems in the 90-ies, when moving scsi disks from one scsi host adapter to another type, *way* before virtualization became a thing. BTW: One possible way to figure which LCHS layout a disk uses is to check the MBR partition table. With that we (a) don't need a new interface between qemu and seabios and (b) it is not needed to manually specify the geometry. cheers, Gerd