{"id":87364,"date":"2020-07-07T13:42:29","date_gmt":"2020-07-07T11:42:29","guid":{"rendered":"https:\/\/prohoster.info\/blog\/administrirovanie\/nastraivaem-drbd-dlya-replikaczii-hranilishha-na-dva-centos-7-servera"},"modified":"2020-07-07T13:42:29","modified_gmt":"2020-07-07T11:42:29","slug":"nastraivaem-drbd-dlya-replikaczii-hranilishha-na-dva-centos-7-servera","status":"publish","type":"post","link":"https:\/\/prohoster.info\/en\/blog\/administrirovanie\/nastraivaem-drbd-dlya-replikaczii-hranilishha-na-dva-centos-7-servera","title":{"rendered":"Setting up DRBD for storage replication on two CentOS 7 servers","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p><b><i>This article's translation was prepared in anticipation of the course launch <noindex><a rel=\"nofollow\" href=\"https:\/\/otus.pw\/17x7\/\">Linux Administrator: Virtualization and Clustering<\/a><\/noindex>.<\/i><\/b><\/p>\n<p>\nDRBD (Distributed Replicated Block Device) is a distributed, flexible, and versatile data storage solution for Linux. It mirrors the contents of block devices, such as hard drives, partitions, logical volumes, etc., between servers. It creates copies of data on two storage devices so that in case of a failure of one, the data on the second can be used.<\/p>\n<p>One could say that it is somewhat like <noindex><a rel=\"nofollow\" href=\"https:\/\/www.tecmint.com\/create-raid1-in-linux\/\">a network RAID configuration<\/a><\/noindex> 1 with disks mirrored across different servers. However, it does not operate the same way as RAID (even network RAID).<noindex><a rel=\"nofollow\" name=\"habracut\"><\/a><\/noindex><\/p>\n<p>Originally, DRBD was primarily used in high availability (HA) clusters; however, starting with version nine, it can be utilized for deploying cloud storage solutions.<\/p>\n<p>In this article, we will explain how to install DRBD on CentOS and briefly demonstrate how to use it for storage (partition) replication on two servers. This is an ideal article to get started with DRBD on Linux.<\/p>\n<h3>Test Environment<\/h3>\n<p>\nWe will use a two-node cluster for this setup.<\/p>\n<ul>\n<li>Node 1: 192.168.56.101 \u2013 tecmint.tecmint.lan<\/li>\n<li>Node 2: 192.168.56.102 \u2013 server1.tecmint.lan<\/li>\n<\/ul>\n<p><\/p>\n<h4>Step 1: Installing DRBD packages<\/h4>\n<p>\nDRBD is implemented as a Linux kernel module. It acts as a driver for a virtual block device, so it is located at the bottom of the system's I\/O stack.<\/p>\n<p>DRBD can be installed from ELRepo or EPEL. Let\u2019s start by importing the ELRepo package signing key and enabling the repository on both nodes as shown below.<\/p>\n<pre><code class=\"bash\"># rpm --import https:\/\/www.elrepo.org\/RPM-GPG-KEY-elrepo.org\n# rpm -Uvh http:\/\/www.elrepo.org\/elrepo-release-7.0-3.el7.elrepo.noarch.rpm<\/code><\/pre>\n<p>Then you need to install the DRBD kernel module and utilities on both nodes using:<\/p>\n<pre><code class=\"bash\"># yum install -y kmod-drbd84 drbd84-utils<\/code><\/pre>\n<p>\nIf you have SELinux enabled, you need to configure policies to free DRBD processes from SELinux control.<\/p>\n<pre><code class=\"bash\"># semanage permissive -a drbd_t\n<\/code><\/pre>\n<p>\nAdditionally, if your system has a firewall (firewalld) running, you need to add the DRBD port 7789 to allow data synchronization between the two nodes.<\/p>\n<p>Run these commands for the first node:<\/p>\n<pre><code class=\"bash\"># firewall-cmd --permanent --add-rich-rule='rule family=&quot;ipv4&quot;  source address=&quot;192.168.56.102&quot; port port=&quot;7789&quot; protocol=&quot;tcp&quot; accept'\n# firewall-cmd --reload<\/code><\/pre>\n<p>\nThen run these commands for the second node:<\/p>\n<pre><code class=\"bash\"># firewall-cmd --permanent --add-rich-rule='rule family=&quot;ipv4&quot; source address=&quot;192.168.56.101&quot; port port=&quot;7789&quot; protocol=&quot;tcp&quot; accept'\n# firewall-cmd --reload<\/code><\/pre>\n<p><\/p>\n<h4>Step 2: Preparing low-level storage<\/h4>\n<p>\nNow that we have DRBD installed on both cluster nodes, we need to prepare storage areas of approximately the same size on them. This can be a disk partition (or an entire physical hard drive), a RAID logical device, <noindex><a rel=\"nofollow\" href=\"https:\/\/www.tecmint.com\/create-lvm-storage-in-linux\/\">a logical LVM volume<\/a><\/noindex> or any other type of block device present in your system.<\/p>\n<p>For this article, we will create a test block device of size 2 GB using the dd command.<\/p>\n<pre><code class=\"bash\"># dd if=\/dev\/zero of=\/dev\/sdb1 bs=2024k count=1024<\/code><\/pre>\n<p>\nLet's assume this is an unused partition (\/dev\/sdb1) on the second block device (\/dev\/sdb) connected to both nodes.<\/p>\n<h4>Step 3. Configuring DRBD<\/h4>\n<p>\nThe main DRBD configuration file is <code>\/etc\/drbd.conf<\/code>, while additional configuration files can be found in the directory <code>\/etc\/drbd.d<\/code>.<\/p>\n<p>To replicate storage, we need to add the necessary configurations to the file <code>\/etc\/drbd.d\/global_common.conf<\/code>, which contains global and common sections of the DRBD configuration, while we need to define resources in <code>.res<\/code> files.<\/p>\n<p>Let's back up the original file on both nodes, and then open a new file for editing (use a text editor of your choice).<\/p>\n<pre><code class=\"bash\"># mv \/etc\/drbd.d\/global_common.conf \/etc\/drbd.d\/global_common.conf.orig\n# vim \/etc\/drbd.d\/global_common.conf <\/code><\/pre>\n<p>\nAdd the following lines to both files:<\/p>\n<pre><code class=\"bash\">global {\n usage-count  yes;\n}\ncommon {\n net {\n  protocol C;\n }\n}<\/code><\/pre>\n<p>\nSave the file, then close the editor.<\/p>\n<p>Let's pause briefly at the line protocol C. DRBD supports three different replication modes (i.e., three degrees of replication synchronization), namely:<\/p>\n<ul>\n<li>protocol A: asynchronous replication protocol; most often used in long-distance replication scenarios.<\/li>\n<li>protocol B: semi-synchronous replication protocol or synchronous memory protocol.<\/li>\n<li>protocol C: commonly used for nodes in networks with short distances; this is undoubtedly the most frequently used replication protocol in DRBD setups.<\/li>\n<\/ul>\n<p>\n<b>Important<\/b>: <i>The choice of replication protocol affects two deployment factors: protection and latency. Conversely, throughput is not significantly dependent on the chosen replication protocol.<\/i><\/p>\n<h4>Step 4. Adding a Resource<\/h4>\n<p>\nA Resource is a collective term that refers to all aspects of a specific replicated dataset. We will define our resource in the file <code>\/etc\/drbd.d\/test.res<\/code>.<\/p>\n<p>Add the following to the file on both nodes (don't forget to replace the variables with actual values for your environment).<\/p>\n<p>Pay attention to the host names; we need to specify the network host name, which can be obtained using the uname command. <code>-n<\/code>.<\/p>\n<pre><code class=\"bash\">resource test {\n        on tecmint.tecmint.lan {\n \t\tdevice \/dev\/drbd0;\n       \t\tdisk \/dev\/sdb1;\n        \t\tmeta-disk internal;\t\n                \taddress 192.168.56.101:7789;\n        }\n        on server1.tecmint.lan  {\n\t\tdevice \/dev\/drbd0;\n        \t\tdisk \/dev\/sdb1;\n        \t\tmeta-disk internal;\n                \taddress 192.168.56.102:7789;\n        }\n}\n}<\/code><\/pre>\n<p>\nwhere:<\/p>\n<ul>\n<li><i>on hostname<\/i>: the section on refers to the nested configuration operator.<\/li>\n<li><i>test<\/i>: this is the name of the new resource.<\/li>\n<li><i>device \/dev\/drbd0<\/i>: specifies a new virtual block device managed by DRBD.<\/li>\n<li><i>disk \/dev\/sdb1<\/i>: this is the partition of the block device that acts as the backup device for the DRBD device.<\/li>\n<li><i>meta-disk<\/i>: defines where DRBD stores its metadata. Internal means that DRBD stores its metadata on the same physical low-level device as the actual data in production.<\/li>\n<li><i>address<\/i>: specifies the IP address and port number of the corresponding node.<\/li>\n<\/ul>\n<p>\nAlso, note that if both hosts have the same values for parameters, you can specify them directly in the resource section.<\/p>\n<p>For example, the above configuration can be restructured as:<\/p>\n<pre><code class=\"bash\">resource test {\n\tdevice \/dev\/drbd0;\n\tdisk \/dev\/sdb1;\n        \tmeta-disk internal;\t\n        \ton tecmint.tecmint.lan {\n \t\taddress 192.168.56.101:7789;\n        \t}\n        \ton server1.tecmint.lan  {\n\t\taddress 192.168.56.102:7789;\n        \t\t}\n}<\/code><\/pre>\n<p><\/p>\n<h4>Step 5. Initialization and starting of the resource<\/h4>\n<p>\nTo interact with DRBD, we will use the following administration tools (which interact with the kernel module for configuring and administering DRBD resources):<\/p>\n<ul>\n<li><i>drbdadm<\/i>: high-level administration tool for DRBD.<\/li>\n<li><i>drbdsetup<\/i>: lower-level administration tool for connecting DRBD devices to their backup devices, configuring pairs of DRBD devices to mirror their backup devices, and checking the configuration of running DRBD devices.<\/li>\n<li><i>Drbdmeta<\/i>: metadata management tool.<\/li>\n<\/ul>\n<p>\nAfter adding all initial configurations for the resource, we need to call the resource on both nodes.<\/p>\n<pre><code class=\"bash\"># drbdadm create-md test<\/code><\/pre>\n<p>\n<img decoding=\"async\" alt=\"Setting up DRBD for storage replication on two CentOS 7 servers\" src=\"\/wp-content\/uploads\/2020\/07\/cf084d17f60a125225f2b75668515d4f.jpg\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<i>Initializing metadata storage<\/i><\/p>\n<p>Next, we need to start it, which will connect the resource to its backup device, then set replication parameters and connect the resource to its peer:<\/p>\n<pre><code class=\"bash\"># drbdadm up test<\/code><\/pre>\n<p>\nNow, if you run the command <noindex><a rel=\"nofollow\" href=\"https:\/\/www.tecmint.com\/commands-to-collect-system-and-hardware-information-in-linux\/\">lsblk<\/a><\/noindex>, you will notice that the DRBD device\/volume drbd0 is linked to the backup device <code>\/dev\/sdb1<\/code>:<\/p>\n<pre><code class=\"bash\"># lsblk<\/code><\/pre>\n<p>\n<img decoding=\"async\" alt=\"Setting up DRBD for storage replication on two CentOS 7 servers\" src=\"\/wp-content\/uploads\/2020\/07\/afb0be2e739c3ce71a556e78c8a55f07.jpg\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<i>List of block devices<\/i><\/p>\n<p>To disable the resource, run:<\/p>\n<pre><code class=\"bash\"># drbdadm down test<\/code><\/pre>\n<p>\nTo check the status of the resource, execute the following command (note that at this stage, the state of the disks is expected) <i>Inconsistent\/Inconsistent<\/i>):<\/p>\n<pre><code class=\"bash\"># drbdadm status test\nOR\n# drbdsetup status test --verbose --statistics \t#for  a more detailed status<\/code><\/pre>\n<p>\n<img decoding=\"async\" alt=\"Setting up DRBD for storage replication on two CentOS 7 servers\" src=\"\/wp-content\/uploads\/2020\/07\/a45da69bfbc4199ef263359b623fdd05.jpg\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<i>Resource status check on the<br \/>\nsides<\/i><\/p>\n<h4>Step 6: Setting the primary resource\/source for initial device synchronization<\/h4>\n<p>\nAt this stage, DRBD is already ready for operation. Now we need to specify which node should be used as the source for initial device synchronization.<\/p>\n<p>Run the following command only on one node to initiate the initial full synchronization:<\/p>\n<pre><code class=\"bash\"># drbdadm primary --force test\n# drbdadm status test<\/code><\/pre>\n<p>\n<img decoding=\"async\" alt=\"Setting up DRBD for storage replication on two CentOS 7 servers\" src=\"\/wp-content\/uploads\/2020\/07\/6505d6350609e03da02f30eeafecd72c.jpg\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<i>Setting the primary node as the initial device<\/i><br \/>\nAfter synchronization is complete, the status of both disks should be UpToDate.<\/p>\n<h4>Step 7: Testing the DRBD setup <\/h4>\n<p>\nFinally, we need to check whether the DRBD device will function as needed for storing replicated data. Remember that we used an empty disk volume, so we must create a filesystem on the device and mount it to see if we can use it for storing replicated data.<\/p>\n<p>We need to create a filesystem on the device using the following command on the node from which we started the initial full synchronization (the one with the resource having the primary role):<\/p>\n<pre><code class=\"bash\"># mkfs -t ext4 \/dev\/drbd0<\/code><\/pre>\n<p>\n<img decoding=\"async\" alt=\"Setting up DRBD for storage replication on two CentOS 7 servers\" src=\"\/wp-content\/uploads\/2020\/07\/32c9ac65a06993e58d9ce3b568fadca1.jpg\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<i>Creating a filesystem on the Drbd volume<\/i><\/p>\n<p>Then mount it as shown (you can give the mount point an appropriate name):<\/p>\n<pre><code class=\"bash\"># mkdir -p \/mnt\/DRDB_PRI\/\n# mount \/dev\/drbd0 \/mnt\/DRDB_PRI\/\n<\/code><\/pre>\n<p>\nNow copy or create some files in the above mount point and make a long listing using <noindex><a rel=\"nofollow\" href=\"https:\/\/www.tecmint.com\/tag\/linux-ls-command\/\">the ls command<\/a><\/noindex>:<\/p>\n<pre><code class=\"bash\"># cd \/mnt\/DRDB_PRI\/\n# ls -l <\/code><\/pre>\n<p>\n<img decoding=\"async\" alt=\"Setting up DRBD for storage replication on two CentOS 7 servers\" src=\"\/wp-content\/uploads\/2020\/07\/a32321e2b5c587215dc06d2b3960a4bc.jpg\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<i>Output a list of the contents of the primary Drbd volume<\/i><\/p>\n<p>Next, unmount the device (make sure the mount is not open, change the directory after unmounting to avoid errors) and change the role of the node from primary to secondary:<\/p>\n<pre><code class=\"bash\"># umount \/mnt\/DRDB_PRI\/\n# cd\n# drbdadm secondary test<\/code><\/pre>\n<p>\nMake the other node (which has the resource with the secondary role) primary, then connect to it and perform a long listing of the mount points. If the setup works correctly, all files stored on the volume should be there:<\/p>\n<pre><code class=\"bash\"># drbdadm primary test\n# mkdir -p \/mnt\/DRDB_SEC\/\n# mount \/dev\/drbd0 \/mnt\/DRDB_SEC\/\n# cd \/mnt\/DRDB_SEC\/\n# ls  -l <\/code><\/pre>\n<p>\n<img decoding=\"async\" alt=\"Setting up DRBD for storage replication on two CentOS 7 servers\" src=\"\/wp-content\/uploads\/2020\/07\/c54d7754a01987765a19b5bde95fc555.jpg\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<i>Checking the DRBD setup running on the secondary node.<\/i><\/p>\n<p>For more information, refer to the administration tool documentation pages:<\/p>\n<pre><code class=\"bash\"># man drbdadm\n# man drbdsetup\n# man drbdmeta<\/code><\/pre>\n<p>\nNote: <noindex><a rel=\"nofollow\" href=\"https:\/\/docs.linbit.com\/docs\/users-guide-8.4\/\">DRBD User Guide<\/a><\/noindex>.<\/p>\n<h4>Summary<\/h4>\n<p>\nDRBD is extremely flexible and versatile, making it a storage replication solution suitable for adding HA to virtually any application. In this article, we showed how to install DRBD on CentOS 7 and briefly demonstrated how to use it for storage replication. Feel free to share your thoughts with us using the feedback form below.<\/p>\n<p>\n<noindex><a rel=\"nofollow\" href=\"https:\/\/otus.pw\/17x7\/\">Learn more about the course.<\/a><\/noindex><\/p>\n<p>Source: <a content=\"nofollow\" rel=\"nofollow\" href=\"https:\/\/habr.com\/ru\/company\/otus\/blog\/509710\/\">habr.com<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"<p>\u041f\u0435\u0440\u0435\u0432\u043e\u0434 \u0441\u0442\u0430\u0442\u044c\u0438 \u043f\u043e\u0434\u0433\u043e\u0442\u043e\u0432\u043b\u0435\u043d \u0432 \u043f\u0440\u0435\u0434\u0434\u0432\u0435\u0440\u0438\u0438 \u0441\u0442\u0430\u0440\u0442\u0430 \u043a\u0443\u0440\u0441\u0430 \u00ab\u0410\u0434\u043c\u0438\u043d\u0438\u0441\u0442\u0440\u0430\u0442\u043e\u0440 Linux. \u0412\u0438\u0440\u0442\u0443\u0430\u043b\u0438\u0437\u0430\u0446\u0438\u044f \u0438 \u043a\u043b\u0430\u0441\u0442\u0435\u0440\u0438\u0437\u0430\u0446\u0438\u044f\u00bb. 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\u0431\u043b\u043e\u0447\u043d\u044b\u0445 \u0443\u0441\u0442\u0440\u043e\u0439\u0441\u0442\u0432, \u0442\u0430\u043a\u0438\u0445 \u043a\u0430\u043a \u0436\u0435\u0441\u0442\u043a\u0438\u0435 \u0434\u0438\u0441\u043a\u0438, \u0440\u0430\u0437\u0434\u0435\u043b\u044b, \u043b\u043e\u0433\u0438\u0447\u0435\u0441\u043a\u0438\u0435 \u0442\u043e\u043c\u0430 \u0438 \u0442.\u0434. \u043c\u0435\u0436\u0434\u0443 \u0441\u0435\u0440\u0432\u0435\u0440\u0430\u043c\u0438. \u041e\u043d\u043e \u0441\u043e\u0437\u0434\u0430\u0435\u0442 \u043a\u043e\u043f\u0438\u0438 \u0434\u0430\u043d\u043d\u044b\u0445 \u043d\u0430 [&hellip;]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":87365,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[688],"tags":[],"class_list":["post-87364","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-administrirovanie"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 5.0.2 - aioseo.com -->\n\t<meta name=\"description\" content=\"\u041f\u0435\u0440\u0435\u0432\u043e\u0434 \u0441\u0442\u0430\u0442\u044c\u0438 \u043f\u043e\u0434\u0433\u043e\u0442\u043e\u0432\u043b\u0435\u043d \u0432 \u043f\u0440\u0435\u0434\u0434\u0432\u0435\u0440\u0438\u0438 \u0441\u0442\u0430\u0440\u0442\u0430 \u043a\u0443\u0440\u0441\u0430 \u00ab\u0410\u0434\u043c\u0438\u043d\u0438\u0441\u0442\u0440\u0430\u0442\u043e\u0440 Linux.\" \/>\n\t<meta name=\"robots\" content=\"max-image-preview:large\" \/>\n\t<meta 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