Re: [Qemu-block] RFC iscsi: set FUA and DPO if !bs->enable_write_cache

[Kevin Wolf]

Am 15.04.2015 um 11:03 hat Paolo Bonzini geschrieben:
> > cachemode unsafe avoids the explicit flush which is no good idea as
> > we all would agree.
> 
> Actually, in the case of battery-backed cache file.cache.no-flush=on
> (aka file.cache=unsafe) _is_ a good idea, because arrays with
> battery-backed cache ignore flushes (just like FUAs).
> 
> Of course cache=unsafe and cache.no-flush=on are not a good idea because
> you want to flush the qcow2 caches for example.

Actually, cache=unsafe doesn't disable qcow2 cache writeback. That's the
difference between .bdrv_co_flush_to_os as used by image formats and
.bdrv_co_flush_to_disk/.bdrv_aio_flush used by the protocol layer; only
the latter is disabled.

So cache=unsafe should be fine (and file.cache.* doesn't work yet, but
I'm working on it at the moment).

Kevin