Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD

[Peter Maydell]

On 17 March 2013 18:51, Paolo Bonzini <address@hidden> wrote:
> Il 17/03/2013 01:04, Aurelien Jarno ha scritto:
>>                           | boot | install build-dep | build lm-sensors |
>>   ------------------------+------+-------------------+------------------+
>>   versatile               | 1:09 |             2:27  |             4:09 |
>>   versatile cache=wb      | 1:08 |             2:25  |             3:44 |
>
> Strange, cache=wb should be the default.
>
> The real problem with SD is that it doesn't have a flush command, hence
> it cannot be made safe against power losses.

So, two things here:
(a) the way to make it safe against power loss is that when the
guest writes a block of data it has to really hit the emulated
disk, because this is how the hardware works
(b) I thought this was the reason cache=wb wasn't the default (ie
that we weren't defaulting to 'may lose data on powerloss'). At the
time I last looked into command line options for these boards I'm
pretty sure it wasn't the default, because the performance improvement
from turning on caching was huge.

-- PMM