VMware ESXi vs XenServer

A run through the pros and cons of VMware ESXi and Citrix XenServer. And why we redeem ESXi for XenServer.

A year or so ago, we at RouteYou bought a new PC to do data processing. Since we use all sorts of software, some running on Windows other on Linux, we decided to use virtualization for that one PC. It would give us the flexibility to let each developer pick the right tools for the job, and still be able to offload the processing to that one PC.

It all started with VMware Server installed on Ubuntu 8.04, but that turned out to be not such a performant solution. Then came the day VMware made ESXi free to use. After some hardware compatibility troubles we managed to get VMware ESXi running on our custom built PC. Life was good, thanks to better performance and easy administration through the excellent VMware Infrastructure Client. But we did realise that all that administration goodness would cease to be free of charge when we’d add a second virtual machine host. We would have to administer both machines seperatly, or buy some thousand dollars worth of licenses. Managing both physical hosts seperatly means you can’t easily move a virtual machine from one host to the other, whether the guest is running or not.

A month ago, the moment was there. A second processing PC was being ordered. We made sure it was compatible with VMware ESXI, but we had a wry sense about having to mis the flexibility of moving virtual machines around. So we started to look for other options and came across XenServer.

Both the free versions of VMware ESXi and Citrix XenServer have :

  • Support for Windows and Linux guests
  • Unlimited servers, virtual machines and memory
  • P2V & V2V conversion
  • Shared SAN and NAS storage

But XenServer adds some more features to its free offer :

  • Centralized multi-server management
  • Live motion
  • Shared virtual machine template library
  • Centralized configuration management

With VMware those extra options (not including live motion) would cost us around €1000 per physical server, which is almost the price of the hardware. So we started to experiment with XenServer to see if it could live up to the expectations. It didn’t take long before we started to see the differences between ESXi and XenServer :

  • In VMware Infrastructure Client you can have different users, and assign them permissions to start and stop their virtual machines. That’s not possible with XenServer.
  • With ESXi you can allocate more memory to virtual machines than you physically have available. They call it memory overcommit. Ofcourse this gets really slow when all that memory is actually used. So I find myself still wondering if the lack of this feature in XenServer is all that bad.

3 thoughts on “VMware ESXi vs XenServer”

  1. Thank you. Also, Rhel 5.4 is not supported by XenServer yet!!

    However, I’ve done a simple disk performance test between XenServer & ESXi, which show ESXi has very slow performance compared to XenServer.

    I transfer a 3.5G file ( Rhel5.4 DVD iso ) from/to XenServer & ESXi ( XenServer Guest: Rhel5.3; ESXi Guest: Rhel5.4) respectively from a third server. ESXi is really slow. I am wondering if anyone has the similiar problem?

    I don’t know if there is any way to improve ESXi performance. If I cannot improve its performance, it seems I need to give up it. Anyone can help ? Is my adapter problem or wrong storage …?

    Following is the test results:
    #########################
    # VMWare ESXi 4.0 u1 @ web1
    #########################
    4vCPU / 4092 MB RAM ( 265.95 Memory Overhead ) / VMware Tools Not installed / 40GB Storage
    Redhat Enterprise 5.4
    VM Network ( Standard switch network )
    Adapter E1000
    LSI Logic parallel

    Input : 12.1MB/s 04:42 for 3408MB file
    Output : 1.4MB/s 39.58 for 3408MB file

    ##########################
    # XenServer @ app1
    ##########################
    1vCPU / 1560MB RAM / 40GB Storage
    Redhat Enterprise 5.3

    Input : 30.7MB/s 01:51 for 3408MB file
    Output : 26.6MB/s 02:08 for 3408MB file

    Drawbacks : wait for template, cannot overcommit

  2. I am finding the opposite about disk performance. I am finding that VMWare ESXi disk write performance is about 2.5 times as fast for the same guest OS (Centos 5.3) as for Xenserver. In both cases, the storage hardware is an Equallogic iSCSI SAN. My test is very simple:

    dd if=/dev/zert of=/tmp/test.txt bs=2G count=1

    On this test on VMWare I get 190 MB/sec and with XenServer 70 MB/sec.

    I really want to use Xenserver because of the free centralized managment console, but I am not sure if I can tolerate this degradation in disk performance.

  3. I run ESXi 5.0 at home. I tested Xenserver as well. It worked just fine, but it was a little weird when it came to the console. The graphics were pixelated, it looked like I was connecting with LogMeIn, even though I was local. Anyway I was wondering what you guys ended up going with?

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