Wednesday, January 8, 2014

Xen learnings

This week, I was trying to get my head around a new Hypervisor(new for me, obiviously), ie XenServer. Though it is pretty much same as ESXi and is free as well, there are some striking differences as well.The observations are based on the free version of Citrix XenServer version 6.2.0

- While ESXi needs a paid vCenter to manage multiple hosts, you can use the free XenCenter software to manage multiple Xen hosts

- Latest version of Xen server doesnt have the equalent of DRS or DPM. There was a feature named workload balancing, which was strangely discontinued in version 6.2.0 stating reason that there are no takers for it.

- It does offer a High Availability of VMs using pool based clustering of hosts

-XenMotion is the equalent of VM live migration, but it is restricted to one VM at a time

-XenCenter doesnt have a web client like vCenter

-There was a tool named XenConvert used for physical to virtual conversion, but it is retired as well.

-There is an option named Dynamic Memory Control(DMC), which can be used for dynamic allocation of memory for VMs. We can set a maximum and minimum memory options for VMs which will be used by XenServer to manage memory crunch situations

-Thin provisioning is supported  for local storages only

-Distributed vSwitch controller appliance  is available for centralized management of networks in XenCenter. However, this too is being depreciated in v6.2.0

PS: One interesting point to note is that the configuration limits document of xenServer is very small when compared to VMware and it doesnt have much details mentioned. For example, VMware specified the maximum number of vCPUs that we can create per physical processor core. For v5.1 its 25 and for v5.5 its 32. However Xen doesnt give you a hardcoded value for that. When we contacted Xen support regarding the same, they mentioned that there is no limit!!! Obiviously, that means you have to keep performance in mind while deciding on the number of vCPUs

Here is a good comparison matrix between various hypervisors available in market

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