Am 12.02.2013 11:01, schrieb Gordan Bobic: > On 12/02/2013 00:42, Reindl Harald wrote: >> under real load the XEON is so much faster even >> with the virualization overhead which is small >> these days but still exists > > Small as in un-noticeable if your VMs are largely idling. Not that small if you intend to push the hardware to it's > actual limits. On a Core2 class machine, the best hypervisors manage to do it with about a 25% performance drop. > Many do worse. > > http://www.altechnative.net/2012/08/04/virtual-performance-part-1-vmware/ there is never 25% performance drop in case of CPU this may be true for IO and even this depends heavily on the storage, a dedicated SAN storage with 1 GB writeback cache will outperform in most cases you local disks because finally you invest much more money and disks in a shared spindle and the dimension is for your whole infrastructure while most guests are not the whole day busy, the same for CPU means: you buy much better hardware with more and faster CPU's for a single device as you would buy for 20 machines and most of the day one or two guests can allocate most of the ressources on their own >> i have seen the XEON machine with a Load of 140 while a massive DDOS was running >> with ten thousands of connections and 100Mbit incoming traffic from always the >> same request on a mysql-driven website and ssh/lsof/ps aux was as fast as it would >> be idle, on the home-machine with a load over 40 you are done > > It's not that clear cut - it depends on where the DOS bottlenecks the system. If you have a web server being DOS-ed > and it's waiting for responses from MySQL which is on a different server, then yes, you'll have a very high load > and very low CPU usage since most of the httpds are waiting for a response from the DB. Since CPU usage is low, the > machine itself will be very responsive if you ssh into it. The web response, may well not be. it is a clear cut the DB was on the same VM the VM had as much virtual CPU's as the host both, the host and the VM had 100% CPU load
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