Re: [Qemu-devel] Default cache mode

[Kevin Wolf]

Am 29.06.2011 14:06, schrieb Anthony Liguori:
> On 06/29/2011 06:59 AM, Kevin Wolf wrote:
>> Hi,
>>
>> I think we have touched this topic before during some IRC discussions or
>> somewhere deep in a mailing list thread, but I think it hasn't been
>> discussed on the list.
>>
>> Our default cache mode of cache=writethrough is extremely conservative
>> and provides absolute safety at the cost of performance,
> 
> But for the most part, we track bare metal fairly well in terms of block 
> performance, no?
> 
> Or are you really referring to qcow2 as a specific example?  In the 
> past, we used a different default caching mode for qcow2.  I think that 
> could be done again if there was a compelling reason.

No, people are also complaining about bad performance with raw. Which
isn't really surprising when you do a flush after each single write
request. O_SYNC is really much more than is needed in the average case.

Kevin