Re: Expected Behavior

[Jonathan Tripathy <jonnyt-Nf8S+5hNwl710XsdtD+oqA@public.gmane.org>]

On 30/08/2012 08:15, Jonathan Tripathy wrote:
> Hi There,
>
> On my WIndows DomU (Xen VM) which is running on a LV which is using 
> bcache (against two SSD in MDRAID1 and a MD-RAID10 spindle array), I 
> ran an IOMeter test for about 2 hours (with 30 workers and a io depth 
> of 256). This was a very heavy workload (Got an average iops of about 
> 6.5k). After I stopped the test, I then went back to fio on my Linux 
> Xen Host (Dom0). The random write performance isn't as good as it was 
> before I started the IOMeter test. It used to be about 25k and now 
> showed about 7k iops. I assumed that maybe this was due to the fact 
> that bcache was writing out dirty data to the spindles so the SSD was 
> busy.
>
> However, this morning, after the spindles have calmed down, 
> performance of fio is still not great (still about 7k).
>
> Is there something wrong here? What is expected behavior?
>
> Thanks
>
BTW, I can confirm that this isn't an SSD issue, as I have a partition 
on the SSD that I kept seperate from bcache and I'm getting excellent 
(about 28k) iops performance there.

It's as if after the heavy workload I did with IOMeter, bcache has 
somehow throttled the writeback cache?

Any help is appreciated.