| Chris Ross on 28 Oct 2006 18:16:04 -0000 |
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I have been running VMWare for several years with with good success. We ran some servers in VMs that were running ~100% processor utilization all day long and they were quite stable. Before going to Xen, I would like to see a better management interface. For a lower level admin, Xen can be a bit problematic. VMWare has been really easy to deal with Currently, we are running VMWare Server and ESX server 2.5.3. In the January February time frame, we will be getting hardware to implement VI3 largely for a DR site. Our primary consideration for waiting to implement VI3 is the line of quad core Xeon procs. that are going to be released. That is something you may want to consider. Our VMWare server implementation have been on Dell 750s and Dell 2850s. Most of the deployments were on CentOS 4. A couple of implementation were on windows. We will probably get rid of the Windows hosts and reload them with CentOS. We have not seen any significant difference between the Windows and Linux host OS. If you are going to collect stats on the running VMs, you may want to go the Windows route. There is no way to get good info on the linux VMWare Server. The Windows version provides a WMI interface that allows you to get some info on memory, network and disk utilization on a per VM basis. With ESX server you get statistical info out of the box. This is really helpfull when you run a number of boxes and try to balance work loads. I strongly agree with the disk IO situation. Virtual disks suffer in the performance area. ESX server with vmfs does perform better. On VMWare Server, you definitely want to allocate all of the disk space. Don't use growable volumes if you want performance. If you are going to have high disk io loads, you can allocate a disk partition directly to the VM. By allocating a partition, you get rid of the additional file system overhead. Unfortunately, you can't get rid of the virtual hardware overhead. There are some good posts on forums at VMWare's web site. MS Exchange is a real disk io hog. The folks who are doing enterprise Exchange deployments seam to install the OS and applications on virtual disks then put the information store and logs one native LUNs. In testing, I tried putting virtual disks on XFS partitions in hope of getting better disk performance. One day, the box went down hard and the guest file system was unrecoverable. The problem is that the guest writes the data to the journal but the journal is not actually written to disk. Since the virtual machine monitor reports that the data was written to disk, the guest has no way to know that the data is still in cache. This will really kill you with a database that is supposed to be durable. If the data is directly written to a LUN, a lot of the durability problem goes away. We have deployed virtual disks on ext3 and NTFS with very little trouble other than the performance issues. Currently we are looking at the concept of using JFS as opposed to ext3. JFS has some compelling features regarding limited caching and the ability to freeze the fs. What we are looking at is means of creating a clean quick snap of the VM. If the guest is shut down then free the file system, we can shoot a clean LVM snap. Unfreeze the fs and power up the guest and you are good to go. Now you can back things up at our leisure. The OS shutdown through boot should take on the order of 30 seconds. I am a bit hesitant to sleep the guest because there are supposed to be problems restoring backups of VMs that are sleeping. With VMWare, the VMWare tools are pretty important to make the entire solution work. The tools allow the host and guest to communicate. If you run Windows on ESX servre with the tools installed, ESX will even be able to use shared memory pages. I don't know if there are any such optimizations for linux guests. If you want to go the Xen route, it may be interesting to look at the OpenSolaris route for the host. That would allow you to use dtrace to see what the VMs are doing. ___________________________________________________________________________ Philadelphia Linux Users Group -- http://www.phillylinux.org Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce General Discussion -- http://lists.phillylinux.org/mailman/listinfo/plug
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