On Sun, May 16, 2010 at 03:34:23PM +0200, Sebastian Herbszt wrote:
Gleb Natapov wrote:
On Sat, May 15, 2010 at 10:08:54PM +0200, Sebastian Herbszt wrote:
Why is a 4 KB physical sector size needed in a VM anyway?
Performance of course. Qemu today can advertise physical block size and logical block size greater then 512 with virtio. The problem is that if logical block size != 512 boot fails.
-- Gleb.
Which OS currently has native support for 4 KB sectors and how big is the performance gain?
I believe at least Linux has it. Windows 7 aligns partition to 4K, so it either has it too, or ready to gain it any moment.
The performance without native support (emulation inBIOS) could be worse due to the additional overhead. How much performance is lost if the 512 byte logical sector size emulation is done in virtio (for reads it could behave like a read ahead buffer) ?
Low performance of BIOS emulation is not a concern. BIOS is used only by boot loaders. OSes access disk without BIOS help.
-- Gleb.