Re: [gentoo-user] how to use my SSD the right way ;-)

[Daniel Troeder]

Am 03.01.2014 15:07, schrieb Alan McKinnon:
> On 03/01/2014 15:13, William Kenworthy wrote:
>> On 03/01/14 15:34, Alan McKinnon wrote:
>>> On 03/01/2014 09:25, Stefan G. Weichinger wrote:
>>>> Am 03.01.2014 07:52, schrieb Alan McKinnon:
>>>>> On 03/01/2014 00:46, Stefan G. Weichinger wrote:
>>>>>> BFQ only for the SSDs ?
>>>>>
>>>>> Yes. The scheduler knows how to deal with SSDs while keeping everything
>>>>> responsive even under load.
>>>>>
>>>>> BFQ seems a good fit for your workcase - desktop/laptop. For those,
>>>>> interactive performance is the most important thing.
>>>>
>>>> So you set BFQ for the SSDs and CFQ for the hdds ? I have both in my
>>>> desktop.
>>>>
>>>>
>>>>
>>>>
>>>
>>> BFQ for both is the recommendation.
>>>
>>> But do try it both ways to see how it performs and compare.
>>>
>>
>> hmm, is BFQ good for VM's too?  I am currently using noops (storage is
>> ceph) and was going to experiment but have not had the time yet.
>
>
> I have no idea, but I'd like to find out.
>
> Instinct tells me one of the host or guest should be NOOP so that the
> other one can get on with scheduling without conflict. But I also reckon
> the question is waaaay more complex than that.
A VM should always use noop, as it doesn't know about the physical
layout of the disk (except if you did pass the devices card through...
with a SAS interface over PCIe for example). What IO-scheduler you'd use
for the host depends on your hardware and the desired optimization goal
(throughput vs latency).

My _personal_ opinion for the desktop(!): If you're content with the
general performance I would not optimize for your most common use case
(global maximum), but for the use case that is not-to-uncommon and that
benefits most of it. The idea is, that if most of you life is good, try
to make the remaining part suck less :)

Greetings,
Daniel