Re: [Qemu-devel] [RFC] Disk integrity in QEMU

[Anthony Liguori]

Ian Jackson wrote:
> Anthony Liguori writes ("[Qemu-devel] [RFC] Disk integrity in QEMU"):
>   
> > So to summarize, I think we should enable O_DSYNC by default to ensure 
> > that guest data integrity is not dependent on the host OS, and that 
> > practically speaking, cache=off is only useful for very specialized 
> > circumstances.  Part of the patch I'll follow up with includes changes 
> > to the man page to document all of this for users.
> >     
>
> I have a patch which does this and allows the host to control the
> buffering with the IDE cache control facility.
>   

Do you mean that the guest can control host disk cachability?  We've 
switched to always use O_DSYNC by default.  There was a very long thread 
about it including benchmarks.  With the right posix-aio tuning, we can 
use O_DSYNC without hurting performance*.

* Write performance drops but only because write performance was greater 
than native before.  It now is at native performance.

Regards,

Anthony Liguori

> I'll be resubmitting it shortly (if I manage to get round to it before
> going away for three weeks on Thursday lunchtime ...)
>
> Ian.
>
>
>