https://backend-engineering-strategy-tools.github.io/site/tags/lvm/Recent content in Lvm on Backend Engineering Strategy ToolsHugo -- gohugo.ioen-usMon, 01 Jan 2024 00:00:00 +0000https://backend-engineering-strategy-tools.github.io/site/public-notes/cloud-infrastructure/lvm/Mon, 01 Jan 2024 00:00:00 +0000https://backend-engineering-strategy-tools.github.io/site/public-notes/cloud-infrastructure/lvm/<p>LVM adds a virtualisation layer between physical disks and filesystems. Instead of formatting a disk partition directly, you assemble physical volumes into a volume group and carve logical volumes out of the pool. This makes resizing, snapshots, and spanning volumes across multiple disks straightforward operations rather than destructive partition table surgery.</p> <h2 id="layers">Layers </h2><table> <thead> <tr> <th>Layer</th> <th>Description</th> </tr> </thead> <tbody> <tr> <td>Physical Volume (PV)</td> <td>A disk or partition initialised for LVM use (<code>pvcreate</code>)</td> </tr> <tr> <td>Volume Group (VG)</td> <td>A pool of storage assembled from one or more PVs</td> </tr> <tr> <td>Logical Volume (LV)</td> <td>A virtual partition carved from a VG, formatted and mounted like a regular disk</td> </tr> </tbody> </table> <div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="color:#75715e"># Initialise two disks as PVs</span> </span></span><span style="display:flex;"><span>pvcreate /dev/sdb /dev/sdc </span></span><span style="display:flex;"><span> </span></span><span style="display:flex;"><span><span style="color:#75715e"># Create a VG from both</span> </span></span><span style="display:flex;"><span>vgcreate data-vg /dev/sdb /dev/sdc </span></span><span style="display:flex;"><span> </span></span><span style="display:flex;"><span><span style="color:#75715e"># Create an LV using all available space</span> </span></span><span style="display:flex;"><span>lvcreate -l 100%FREE -n data-lv data-vg </span></span><span style="display:flex;"><span> </span></span><span style="display:flex;"><span><span style="color:#75715e"># Format and mount</span> </span></span><span style="display:flex;"><span>mkfs.ext4 /dev/data-vg/data-lv </span></span><span style="display:flex;"><span>mount /dev/data-vg/data-lv /mnt/data </span></span></code></pre></div><h2 id="resizing">Resizing </h2><p>The practical benefit over raw partitions: extend a logical volume online without unmounting:</p> <div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="color:#75715e"># Extend the LV by 50GB</span> </span></span><span style="display:flex;"><span>lvextend -L +50G /dev/data-vg/data-lv </span></span><span style="display:flex;"><span> </span></span><span style="display:flex;"><span><span style="color:#75715e"># Grow the filesystem to fill the new space</span> </span></span><span style="display:flex;"><span>resize2fs /dev/data-vg/data-lv </span></span></code></pre></div><h2 id="snapshots">Snapshots </h2><p>LVM supports copy-on-write snapshots. A snapshot captures the LV state at a point in time and stores only the blocks that change afterwards:</p> <div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>lvcreate -L 10G -s -n data-snap /dev/data-vg/data-lv </span></span></code></pre></div><p>Used for consistent backups of live filesystems — snapshot, back up the snapshot, remove it. Rook/Ceph and cloud providers use similar snapshot semantics at the storage layer.</p> <h2 id="resources">Resources </h2><ul> <li><a class="link" href="https://sourceware.org/lvm2/" target="_blank" rel="noopener" >LVM2 documentation</a></li> <li><a class="link" href="https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/9/html/configuring_and_managing_logical_volumes/" target="_blank" rel="noopener" >Red Hat LVM administration guide</a></li> </ul>