[CentOS-virt] i386 VM on x86_64 host in Xen

Tue Dec 11 01:12:11 UTC 2007
Scott Dowdle <dowdle at montanalinux.org>


I see these problems with Xen... and many people are stating that they are running CentOS on CentOS... ie Linux on Linux virtualization... so I thought I'd pipe up and mention OpenVZ again.  It does Linux on Linux virtualization well and allows for i386 guests on x86_64 hosts just fine.

On a dual quad-core Xeon with 16GB of RAM (4GB of swap) I asked the vzsplit command how many machines it thinks my hardware is capable of.  Here's the output:

[root at comp2 ~]# vzsplit -n 9999999
On node with 20114 Mb of memory (RAM + swap) 9999999 VEs can not be allocated
The maximum allowed value is 3795

On a machine with 2GB of RAM and 4GB of swap:

[root at backup1 root]# vzsplit -n 9999999
On node with 6119 Mb of memory (RAM + swap) 999999 VEs can not be allocated
The maximum allowed value is 639

Of course, there are some situations where OpenVZ (ie OS Virtualization) isn't suitable... but for the vast majority of common server tasks, it is.  I don't claim you should try that many virtual machines on a single host node but it just goes to show you the density differences possible between Xen and OpenVZ, eh? :)

Scott Dowdle
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