Write caching on disk indise VM and FLUSH_BUFFERS command.

this bit complex try best explain behavior saw.

i've win2k8 r2 running hyper-v a win2k8 vm (child partition)running exchange 2007 sp1. i'm using 2 fixed size vhd exchange logs , store dbs each. these 2 vhds on seperate disks on hyper-v host. trying understand how write flush by exchange happening inside vm handled parent partition. means when irp_mj_flush_buffers issued inside vm, how parent partition handle it. found when flush happens inside vm, parent partion honor them if disk policy inside the vm set better performance and "enable write caching on disk" set. but when disk write caching disabled inside vm , when write-through write/flushfilebuffers() happens, don't see irp_mj_flush_buffers command @ kernel level in parent partition. confusing me expected hyper-v parent partition honor flush if write cache disabled disk inside vm. wrong here? 1 has idea going on.

imo, can open file non-cache flag, (write) io operations execute (i.e. no io coalescing take place).

in case – if enable cache – see irp_mj_flush_buffers commands (there flush!)

if (write) cache “disabled” – won’t see them – there nothing flush, right?

 

obviously, might wrong ;-(

might better ask in sql or core c++ forums…

 

bottom line – there nothing worry about.

if wrong there – it’ll make impossible run database engine reliably inside vm , see consequences right away. ;-)

Windows Server  >  Hyper-V