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[Xen-users] Re: performance problem with more than one domain U

----Messaggio originale----
Da: todd.deshane@xxxxxxx
Data: 25/09/2011 4.37

> So the VMs have very different configurations then?
> Have you tried giving the 2 VMs equal resources?
> Why wouldn't you expect a virtual machine with less vCPUs and less memory
> to perform slower?

OK, maybe I did not explain very well the situation in my previous post.

Let's say I have 2 VM, called VM "A" and VM "B"

VM "A" has 8 vcpus and 12 GB RAM

VM "B" has  1 vcpu and 2 GB RAM

Now, I start the VM A and from the VM A I do the command time rm -r  /mydir
and I have this time:

0.15 user 
0.60 system 
3:46.79 elapsed

Then I start the VM "B". I just start it, but I am always logged to VM "A".

At this point I launch another time the command "time rm -r  /mydir" ALWAYS
FROM VM "A", not B!
And, on the same VM, this time I have:
0.00 user 
0.56 system 
15:33.38 elapsed

The only difference is that now domain "B" is running.

>The rm command might not get the best benchmark to to understand what
>is going on. Have you considered testing a microbenchmark like iozone?

I also did the command:

hdparm -tT /dev/mapper/myserver-root

Strange thing, this always perform similar

when the rm command took 8:42 minutes:
 Timing cached reads:   5700 MB in  1.99 seconds = 2857.98 MB/sec
 Timing buffered disk reads:  120 MB in  3.02 seconds =  39.75 MB/sec

when the rm command took 1:27 minutes:
 Timing cached reads:   5466 MB in  1.99 seconds = 2740.00 MB/sec
 Timing buffered disk reads:  146 MB in  3.01 seconds =  48.48 MB/sec

>What is your disk backend and is it the same for each? It is a shared
>directory or are you creating/copying the same directory to each
>machine for the test?

As explained above it is the same VM.

I should add that at hardware level (i.e. dom0) I have an Adaptec Raid Card
with four 2 GB SATA hard disks in a RAID 10 configuration, if that's matter

Thank You for everything


PS: I am sorry, I have some problem with my webmail. So I posted this 3
times ... :-(

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