KVM scalability and consolidation ratio: cache none vs cache writeback

Written by Gionatan Danti on . Posted in Virtualization

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Conclusions

It is clear that enabling caching/buffering is very beneficial to the specific workload tested in this article. Cache led to much higher disk usage and, as often the disk subsystem is the weak link of any server, this mean higher potential consolidation ratio.

The story don't ends here, obviously: sometime RAM capacity plays an even bigger role in defining max consolidation ratio. And Linux is very well equipped in this area, thanks to KSM.

Anyway, anything that increase disk speed is surely welcomed ;)

Feel free to discuss this article with me writing at This email address is being protected from spambots. You need JavaScript enabled to view it.

Have a nice day!

 

Comments   

 
#1 Troels Arvin 2014-01-20 20:24
Where can one read more about the potential issues with write barriers and live migration?
 
 
#2 Gionatan Danti 2014-01-21 10:20
Quoting Troels Arvin:
Where can one read more about the potential issues with write barriers and live migration?


Hi,
here you can find some informations on barriers:
http://www.ilsistemista.net/index.php/virtualization/23-kvm-storage-performance-and-cache-settings-on-red-hat-enterprise-linux-62.html?start=2

On live migration and why it is better to not use it with caching, you can read libvirt and qemu man page.

Regards.
 

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