Storage practice: how to connect servers to the SAN Environment

Connecting a host to a New SAN (storage LAN) is not just like connecting to a separate disk or even a directly connected SCSI Array. This article will explain the principles behind the current best connection method and how to set your storage to have the best stability.

If you already use a direct-connected storage array, they will teach you a lot about the storage world. They use LUN (logical unit number) to set the array itself, and then you must process them at the host level. As the storage scale increases, system administrators need to set up their storage systems in a feasible and reliable way. In the past, it was acceptable to allocate a logical unit number of 10 to 20 GB to 10 different partitions, but it would not work until GB.

First, let's take a look at the steps we need to do before creating a file system. Before creating a file system, perform the following steps:

Set the array as described, and assign the logical unit number to the host;

Connect the optical fiber, a switch connecting from the network card to two different optical fiber channel networks;

Correctly set the partitions of the two vswitches so that both the host and the array can view each other;

Make sure you can see all the logical unit numbers;

Set multiple paths: path failure backup;

The last step is to carefully set the operating system and disk array. We will talk about this part soon.

There is no need to explain how to connect to the optical fiber. We assume that we know how to keep each "path" on the storage of different optical fiber channel networks. Partitioning A vswitch requires more knowledge, but it depends on the actual situation of different vendors. Brocade, McData, and Cisco vswitches are quite different, but the concept is universal. Determine how to partition and make corresponding settings.

Now, you should be able to "see" the new logical unit number on the server. In Windows, the new volumes are displayed when you open the Resource Manager (some reports that you need to restart ). In Linux, at least in the latest version, the new logical unit number will soon be displayed. On Solaris, you need to run the "mongoadm" command, or you may need the "devfsadm" command to see the new logical unit number.

If you only have one path to the storage, you are almost at this step-now start to build a file system. However, most SAN-connected hosts have two paths to the logical unit number. Therefore, the host can see the same logical unit number twice, one time for each array End. Because the storage array has two interfaces, they are actually two arrays. The host must pay attention to this situation, that is, they are actually the same volume.

Multi-path is a host-based driver that is combined with the array support program so that you can have redundant connections to the storage array. If you want to create a file system on all the logical unit numbers you see and decide to mount each logical unit number separately, your disk array will (probably) be overwhelmed. Here is a concept about the "master controller" of the array. If a host wants to access the logic unit number on the non-master array End, and does not first "pass" the preferred path, then the array starts self-protection. This is very simple, but it is a good method.

If you set the logical unit number to one LUN for each controller, interactive, as we suggested last time, your host will be able to use half of the logical unit number successfully. The host can create a file system and successfully use each logical unit number, but it can only use the preferred controller. A controller or switch failure may occur unless half of the volumes disappear. What we really want is to abstract the device path and mount the abstract device. Using a multi-path device node means that the "real" device can disappear at any time, and as long as the driver works well with the disk array, the operating system will not see the mounted disk device disappear.

In fact, it is not easy to set multiple paths. To make it easier, you can use the Veritas Volume Manager disk management software with DMP (dynamic multi-path) function. This software can run on all operating systems and has the same functionality. When you need to migrate volumes between platforms, if you use an OS-neutral file system, you can get twice the result with half the effort.

If you cannot use DMP, you have two other options. The first is to try to get the driver from the storage manufacturer. If the array you purchased includes support software for your operating system, you probably only need to install the vendor's driver and then run it. If not, you have to try using the various multi-path drivers of your operating system.

For example, Solaris has a good support for multi-path drivers. When using the storage supported by Sun, this driver is very useful, but it may not work for other storage. Therefore, this is risky. before purchasing an array, we recommend that you perform a thorough investigation.

Once multiple paths are set, you will have a set of devices that can be freely controlled. Now the real devices are abstracted, so you need to make sure that you are using multiple path device nodes instead of physical paths.

Now it's interesting. Now you plan and design a file system. Be very careful here, because even if there is a flexible disk management tool like Vertias or ZFS, once an incorrect decision is made, there will be no return. How to determine the file system is based on the use of the situation, so the best advice is to think twice. Most people want to combine some logical unit numbers to form a large file system, but do not use the normal time for backup. A large file system also means that it takes more time to repair the damage.

Of course, do not forget to save your vswitch and array settings, multiple paths, and file system settings files in a safe place. The best part of multi-path is in the test phase. Move forward, Start copying large files and copying optical fiber!

Summary

Step: Set the array, switch, and multi-path;

Ideally, the same multi-path solution is used on each host. Second, use the driver provided by the vendor. In the last case, the solution provided by the operating system is used.

Running the disk management software and creating a file system must be based on the actual situation. However, if the platform can be consistent, it is best to fail.

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