Zimbra performance under Xen vs VMwareServer

[john99]

Hello,

we intend to install ZCS either under VMware or Xen on a system with Intel VT support.
The host-os will be Debian, the guest-os Debian or Ubuntu.
I heard that most applications do run faster under Xen than under VMware Server (not ESX!)


Question:
What are your experiences? Is the performance of Zimbra installed on VMware Server only
some percents slower, or even factors slower than under Xen?




Any tips (not only performance related) are appreciated very much. Thank you!


John




PS:
I do know that Xen is not a supported environment

[uxbod]

I used to run ZCS under VMWare but switched to Xen 3.1 under a para-virtualised environment. The performance gains are very noticeable indeed due to its memory addressing etc. I certainly would not switch back to VMware. Issues found ? well none to be honest. I did start with 3.0 and it had all sorts of stability issues with a X86_64 Dom-0 but since upgrading to 3.1.2 (sources) these have all disappeared. I am running both Dom-0 and Dom-Us with CentOS 5.1. If you do use Xen then don't use files for the VMs but lvols as you will get far better performance. If you do decide to go the file route then do not use sparse files, pre-allocate instead, as the performance is far more comparable with lvols.

[dijichi2]

Yup, the key here is para-virt. Don't use hardware VT , you probably won't get much if any better performance than vmware, which sucks.

[petrocc]

Originally Posted by john99

Hello,
we intend to install ZCS either under VMware or Xen on a system with Intel VT support.
The host-os will be Debian, the guest-os Debian or Ubuntu.
I heard that most applications do run faster under Xen than under VMware Server (not ESX!)

I used to be a TSE at VMware supporting ESX, and I'm currently running a VMware Server for some friends Startup, and I've played with Xen a little bit. I have a preference for VMware stuff at this point only because I know it better.

That said it is my belief based on studying all three products that between VMware Server on Linux and Xen you will *probably* see little bit of an advantage to running Xen, especially if you run a para-virtualized kernel.

HOWEVER

This is going to depend HIGHLY on what else you will be running along side (meaning in other VMs).

Zimbra is heavily IO bound, and some if it's sub processes use a LOT of CPU. This is generally NOT a good candidate for virtualization for performance reasons, and given the products you're looking at (Xen, I presume the open-source version and VMware Server) you're not doing it to gain access to things like hot migration of running servers.

I suspect that on a loaded system (meaning Zimbra VM and two or three more doing real work) you would not see a lot of difference.

EDITED TO ADD:
Uh. That was almost illiterate.

What I was trying to say was that while Xen may be a bit faster, under a normal mix of VMs on a properly loaded server you won't see much of a difference.

Any tips (not only performance related) are appreciated very much. Thank you!

I'm new to Zimbra, and will be running it in a VM on a VMware Server install, but only for 2-4 people (two right now). If you can give it enough memory, and aren't doing a lot of IO in the other VMs, or have some monster IO channel you should be ok.

[computerfixitguy]

Maybe I shouldn't chime in here because I have never used Zen, but I have been using Vmware Server with Zimbra for 3 years straignt now. It runs great, in fact, ZCS5 is much better at not killing the host like 4.5 did (culprit: logger).

I have about 100 people hitting a 100 GB (grow as needed) VM with 1.3 GB RAM on a SATA 150 Raid 10 with a Athlon X2 4200 CPU 4GB RAM. ZCS is on a Ubuntu 6.06LTS server (it used to be on FC4). The only problem there is the time drifts worse on Ubuntu than it ever did on FC4. I might switch back to RedHat. I have been running 5.06 for a month I guess, and it was 4.x for the last 2+ years. I have 2 other VM's there now but there were 6. System wide we move about 1000 emails a day I would guess and have an inbound SPAM load of about 100,000 per day.

Twice in the last month we had a user claim they were getting a "delayed" message from the server, but I have never seen it.

Of our hundred Users, half use the AJAX UI, the other half use IMAP (Outlook) and a few use the ZCS Offline client.

Zimbra rocks! Xen interests me because of some potential gain, but I am not sure I would see it. I will say this. Linux/Vmware hosts that I have can get 18-20 VM's giong on them. Same with XP64, but Server 03 blows as a host. Its soooo slloooow. We have 9 hosts running Vmware Server and 3 running ESX. I like ESX better, but my kids need to go to college too.

Derek

[BrianA]

with a progress database server on it, and a mail server, and a web server, and a "mess with" server. it runs mighty fine!

For linux OS, I wouldnt have virtualisation any other way.

[nrc]

ESX was outside the scope of the poster's question but I'll chime in for anyone who may be wondering.

We're serving over 1000 users with a Zimbra installation on VMware ESX servers. We have a multi-server installation with separate MTA and LDAP and mailstore. We have a Barracuda spam filter serving as an edge MTA. I'd strongly recommend a separate physical edge MTA for any medium size or larger installation.

Our servers are HP DL380 G5s with 2.3Ghz quad core processors, 20GB of memory and NetApp SAN storage on the back end. Our Zimbra mailstore Virtual Machine is running 64 bit RHEL4 with 2 CPUs and 12GB of memory allocated. Under a workday load of typically 500 sessions, Zimbra is averaging about half that. Almost all of our users are using the web client.

Performance is good. We have had occasional spikes and reports of "server busy" messages that may yet lead us to bump up the VM to four CPUs, but right now we're still getting a feel for what typical usage will look like.

Of course hot server migration is the icing on the cake. Last week we updated all our ESX servers with no service interruptions simply by migrating everything off the server to be patched. We moved our mailstore in the middle of the day with no impact on users.

[petrocc]

Originally Posted by nrc

Our servers are HP DL380 G5s with 2.3Ghz quad core processors, 20GB of memory and NetApp SAN storage on the back end. Our Zimbra mailstore Virtual Machine is running 64 bit RHEL4 with 2 CPUs and 12GB of memory allocated.
Performance is good. We have had occasional spikes and reports of "server busy" messages that may yet lead us to bump up the VM to four CPUs...

Pushing adding processors to your VMs doesn't always have the effect you would expect--if you have a dual CPU VM on a quad core box it has to wait for 2 cores to get free to run. If you have a quad CPU VM it has to wait for 4 cores to be free--at least in 3.0.x (I didn't support 3.5, so I don't know if that is true there, but I don't think they can easily get around it).

Anyway, ESX is some good stuff.

[uxbod]

From a processor perspective, within Xen, you can pin VMs to a particular CPU or set the credit policy so that the ZCS VM obtains more of the overall processor cycles.

With respect to I/O, whether it be under Xen or VMWare, that is very dependant on your underlying infrastructure anyway. If you have the money throw in a couple of 4GB HBAs and a nice disk subsystem and away you go Oh, and don't forget to stack the server out with memory

[nrc]

Originally Posted by petrocc

Pushing adding processors to your VMs doesn't always have the effect you would expect--if you have a dual CPU VM on a quad core box it has to wait for 2 cores to get free to run. If you have a quad CPU VM it has to wait for 4 cores to be free--at least in 3.0.x (I didn't support 3.5, so I don't know if that is true there, but I don't think they can easily get around it).

Yes, that's why I'm generally reluctant to make that move unless there's a clear, demonstrated need. Right now memory is a much tighter resource than
CPU. Zimbra's memory footprint means that there will always be fewer than average guests competing for CPU on whatever host it's on, so that helps.