Understanding Multipath Logic on Linux Servers
Multipath is a fault-tolerance technique that generally aims to back up the connection of physical servers with storage. When there is damage to the fiber cables, it is important that the server does not lose access to the storage and maintains accessibility. That’s why systems like banks and global e-commerce sites use multipath.
Here’s everything you need to know about multipath on Linux.
Identifiers for Multipath Devices on Servers
For multipath, it is also necessary to browse for multipath devices. If you’ve ever heard of theWWID(World Wide Identifier) concept before, it won’t sound too foreign to you.
By default, the names of multipath devices are set to their WWID. This is a system that guarantees that the multipath device is globally unique and immutable. You can set the default naming here with some manipulations to the multipath configuration file by changing theuser_friendly_namessetting.
As an example, you can think of it like this. Imagine you have storage devices connected to your server such as:
If theuser_friendly_namesoption is set to “yes” at this point, the device names will change.
If you have an Ubuntu server that usesvirtualization technologies, you might receive the following outcome. What you must remember here is that the device you wish to control must be a physical device.
After you set theuser_friendly_namesoption toyesin the configuration file, you can check the device name as follows:
Procedure for Consistent Multipath Device Names
The name assigned to the multipath devices by this procedure will be unique to a node. It is not feasible to state that it applies to all nodes. If you want consistent multipath devices on all nodes, set theuser_friendly_namesoption to “no”. You will reduce any troubles in this manner as the devices will no longer have a unique moniker and will instead utilize WWID.
However, in other circumstances, you may wish to design nodes that are both consistent and easier to reach and utilize.
For such a case, you must first install all multipath devices on one machine. You should also disable all multipath devices on other machines after this step. You can run the following commands for this:
With these commands, you will respectively stop the multipath service and clear all multipath device maps. Now become a root user and copy thebindingsfile located in the/etc/multipathdirectory to other machines.
At this point, you will be using thedaemon processes of Linux. After all these steps, you need to run themultipathddaemon again:
Overview of General Features of Multipath Devices
Multipath devices' features and configuration settings are not limited touser_friendly_names. Below you will find information about some other configurations you can make in the/etc/mutipath.conffile:
Of course, not all attributes are limited to these, and each attribute has its own sub-qualities. Moreover, you can use them in tandem with each other. Below is a sample configuration file for you to review:
Logic in Multipath Devices
you could think of multipath devices as physical units. For example, let/dev/mapper/mpathabe the name of a multipath device. This device will act as a physical unit. When you create anLVM(Logical Volume Management), you will also need to edit the/etc/lvm.conffile.
With the configurations you make here, you will need to filter the disks under the multipath devices. If you don’t, LVM will scan the passive path and multipath will start working again, because the active path can automatically change to the passive path.
To prevent this, you could do the following manipulation on the/etc/lvm.conffile:
This command will add loops and remove all devices. However, the process does not end there. After making this change in/etc/lvm.conf, save the file, and update the initrd as well.initrdallows you to perform some manipulations on the RAM disk. The reason you make changes here is to copy them at boot time.
Every time thelvm.confandmultipath.conffiles are updated, it is necessary to perform this update oninitramfs. This is how you get a stable and sustainable server. You should also not forget about the initramfs update, especially if you have made changes to the blacklist and filter attributes.
Importance of a Multipath System
In multipath environments, servers can continue to access disks even if one of the components (HBA, SAN, storage controller) they use fails. This is a matter of particular interest to system and server administrators.
It is very important for high-traffic servers that contain important information, where security protocols must be high. Because if the server of a website with thousands of credit card information or hundreds of thousands of registered customers is inaccessible because only one component malfunctioned, it would be a huge problem.
It is necessary to master the details of all these operations and the sub-attributes of the attributes in the configuration file. This is because making server configurations always involves a risk. For this type of operation, it makes sense to back up everything or run tests on a test server.
If you don’t have a server to test all this on, installing Ubuntu Server is the optimal choice and is pretty simple too.
Need to set up a server? Here’s what you need to know about installing Ubuntu Server on any machine.
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