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.