Shulou(Shulou.com)06/02 Report--

This time, Citrix XenServer7.1 and VMware ESXi 6.5 are compared from a technical point of view, and items of concern to enterprises are compared from an enterprise point of view. It mainly includes market position, underlying stability of server virtualization, management architecture and compatibility analysis.

Market position

The status of VMware in virtualization is similar to EMC in large storage, IBM in minicomputer, Cisco in network, Citirx in virtual desktop, and Oracle in database. It has long been a monopoly in server virtualization and has an absolute advantage, as can be seen in the magic quadrant of Gartner server virtualization in 2016.

Underlying stability of server virtualization

First take a look at the size of the two server virtualization media.

Judging from the media downloaded from the latest version, XenServer is nearly twice as large as VMware, meaning the code may be twice as large as VMware. A smaller code base means that the "affected surface" is smaller and less code needs to be patched, improving reliability and security. The predecessor of ESXi is ESX,ESX, which relies on Linux systems for management functions, which include executing scripts and installing third-party agents for hardware monitoring, backup, or system management.

In order to make the system more stable, VMware removes all management functions from ESXi and receives vCenter for management. This advantage is that the underlying layer can be run with the least performance, the function is more single, and the disk capacity required is the least, so ESXi supports installation and operation on the SD card and installation on the USB disk. Even if the SD card and USB drive are unplugged, the ESXi can still run and the virtual machine can still provide services. This is something that XenServer cannot achieve. As you can see in the following figure, VMware ESXi has only one layer of Hypervisor.

Let's take a look at why XenServer is so big and must use a hard drive to install its system.

As you can see from the above figure, in addition to the Hypervisor provided by Xen, there is also a Control Domain after the installation of XenServer. Generally, what we call Domain0,Domian0 is actually a Centos system, which is 32-bit before 7. 0 and uses 64-bit Centos after 7. 0. So there has always been a saying that the first virtual machine after XenServer installation is Domain0, which is why XenServer needs so much media.

Let's take a look at the purpose of this virtual machine, which is mainly used to simulate the hardware of the virtual machine, including common virtual machine networks and virtual disks, as well as some other drivers. CPU and memory are called directly through Hypervisor, which is consistent with VMware. But there is a fatal disadvantage here. All the performance bottlenecks are on this Domian0. Disks and network cards need to go through Domain0 and then Hypervisor before they can be called to the underlying network cards and disks. Generally, when we install XenServer, we need to allocate 4 vcpu to Domian0, as well as about 20-40GB disk space to store logs.

After understanding some of the basic principles above, let's re-analyze that this architecture may also lead to problems that are unacceptable to our users.

1. Driver problem, general hardware manufacturers will have different drivers for different operating systems, for example, a company's optical fiber network card, VMware and XenServer do not have this driver. At this time, we only need to ask the manufacturer for the driver for VMware, which is generally available, but we have not encountered any situation that is not available yet. But the XenServer driver is very difficult to get, generally need to be compiled by the user, or use the compiled CentOS driver. After a lot of hard work, it has been compiled. When you make some big patches, or when you do the underlying upgrade of server virtualization, the driver will be lost and have to be recompiled. So in daily work, if XenServer does not have a driver and needs to hit it itself, then you need to be careful when patching and upgrading versions!

two。 As for the speed of network card, VMware provides several types of network card, the mainstream E1000 and VMXNET3, VMXNET3 is the most commonly used, you need to install VMware tools to work properly, it is 10GB, and the transmission efficiency will be higher, while the XenServer virtual machine maximum supports 1GB. In order to improve bandwidth, Citrix recommends using multiple networks to separate, or use Microsoft's own software to bind the network card.

3. Disk compact configuration, XenServer7.1 can not simplify virtual machine disk configuration, XenServer7.6 began to support, released on Sept. 6, 2018, not in this XenServer7.1 comparison. Streamlined provisioning can help users save a lot of storage space, and on some projects, it can help users save nearly a million dollars.

Reduced provisioning (thin provision): no matter how large the virtual machine disk is allocated, it depends on how much space is actually occupied, that is, how much is used. On some core business systems, VMware does not recommend that users turn on this feature, but in virtual desktop environments, it can greatly increase disk utilization. Because the performance degradation of the desktop may not be perceived by the user. The following figure shows the usage of a user's thin configuration. The total capacity is 7TB, and the allocated virtual machines occupy 13TB, and the actual usage data is about 6TB. The utilization rate has nearly doubled.

The downside is that there may be IO delays. But in the real environment, storage added cache, and SSD to do acceleration, IO has been able to meet the requirements of virtual desktops. At this time, we should be more concerned about how to improve the utilization of storage. The simplified disk also supports online expansion of virtual machine disk capacity, which can be operated without downtime.

Management architecture

VSphere is composed of ESXi+vCenter. XenServer uses master mechanism, that is, a XenServer is selected from each XenServer as the total management node. The administrator only needs to connect to master. By default, the first XenServer will become master, or it can be specified by setting priority. A big disadvantage of this mechanism is that sometimes after an unexpected master downtime, other XenServer hosts will enter emergency mode, and then the XenServer network card will be lost and the virtual machine network will be interrupted. Therefore, in the project, we are very afraid of the network instability of XenServer. Once this happens, we need to type commands on XenServer. For more information, please see KB https://support.citrix.com/article/CTX129815. At present, there is no good explanation for this situation. However, it is unacceptable for administrators to stop the service of virtual machines on member machines due to problems with master.

On the contrary, the mechanism of vCenter+ESXi is very stable, and a problem must be corrected here. VCenter is just a key to the function, which is not on the vCenter, but on the ESXi itself. What do you mean, vCenter is dead, ESXi functions can still work normally, such as HA and DRS are working normally, a host is down, HA is still in effect. Now in many projects, vCenter is directly deployed in the cluster, the host where vCenter is located is broken, vCenter will immediately run on another host, and the management will remain the same. In the early days, many administrators would create an extra vCenter and use a backup vCenter to take over when the main vCenter dies, which is a cold standby. In vSphere6.5, vCenter HA mechanism is introduced, which can directly use the function of vCenter to copy an image system. When the main vCenter is dead, the image system directly takes over, which belongs to HA hot backup mechanism.

Compatibility

Server virtualization is only the cornerstone of desktop virtualization, desktop virtualization is one of the functions, such as the building has been built, each room can also be used. At this time, fire fighting and means of escape have become the focus of future management. After the system is built, we need to think more about backup and antivirus security.

According to the actual project and official documentation, only Commvault supports XenServer backup in the leader quadrant, while other vendors do not support XenServer virtual machine backup. For VMware ESXi backup, almost all backup vendors support VMware virtual machine backup. Users have plenty of choice to choose a backup solution that is most suitable for the enterprise. Antivirus software does not give an example, similar to backup.

Summary:

This comparison mainly focuses on the features commonly used by some enterprises, while other features such as NSX, vSAN, FT and many other features are not exemplified.

The main value of XenServer now lies in the price. On the road of open source, more vendors have turned to KVM. In terms of business software, VMware is still the best choice, making it easier for enterprises to enter the enterprise private cloud.

At present, there are fewer and fewer people who can troubleshoot and fix problems in XenServer, and more rely on Citrix 800 manufacturers, while VMware has trained a large number of administrators from the school, which is more suitable for the introduction of future administrators of enterprises.

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