2 posts tagged with "storage"

In earlier versions of Harvester (v1.0.3 and prior), Longhorn volumes may get corrupted during the replica rebuilding process (reference: Analysis: Potential Data/Filesystem Corruption). In Harvester v1.1.0 and later versions, the Longhorn team has fixed this issue. This article covers manual steps you can take to scan the VM's filesystem and repair it if needed.

Stop The VM And Backup Volume​

Before you scan the filesystem, it is recommend you back up the volume first. For an example, refer to the following steps to stop the VM and backup the volume.

• Find the target VM.

• Stop the target VM.

The target VM is stopped and the related volumes are detached. Now go to the Longhorn UI to backup this volume.

• Enable Developer Tools & Features (Preferences -> Enable Developer Tools & Features).

• Click the ⋮ button and select Edit Config to edit the config page of the VM.

• Go to the Volumes tab and select Check volume details.

• Click the dropdown menu on the right side and select 'Attach' to attach the volume again.

• Select the attached node.

• Check the volume attached under Volume Details and select Take Snapshot on this volume page.

• Confirm that the snapshot is ready.

Now that you completed the volume backup, you need to scan and repair the root filesystem.

Scanning the root filesystem and repairing​

This section will introduce how to scan the filesystem (e.g., XFS, EXT4) using related tools.

Before scanning, you need to know the filesystem's device/partition.

• Identify the filesystem's device by checking the major and minor numbers of that device.

1. Obtain the major and minor numbers from the listed volume information.

   In the following example, the volume name is pvc-ea7536c0-301f-479e-b2a2-e40ddc864b58.

   harvester-node-0:~ # ls /dev/longhorn/pvc-ea7536c0-301f-479e-b2a2-e40ddc864b58 -al
   brw-rw---- 1 root root 8, 0 Oct 23 14:43 /dev/longhorn/pvc-ea7536c0-301f-479e-b2a2-e40ddc864b58
   

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   The output indicates that the major and minor numbers are 8:0.

2. Obtain the device name from the output of the lsblk command.

   harvester-node-0:~ # lsblk
   NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
   loop0    7:0    0     3G  1 loop /
   sda      8:0    0    40G  0 disk
   ├─sda1   8:1    0     2M  0 part
   ├─sda2   8:2    0    20M  0 part
   └─sda3   8:3    0    40G  0 part
   

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   The output indicates that 8:0 are the major and minor numbers of the device named sda. Therefore, /dev/sda is related to the volume named pvc-ea7536c0-301f-479e-b2a2-e40ddc864b58.

• You should now know the filesystem's partition. In the example below, sda3 is the filesystem's partition.
• Use the Filesystem toolbox image to scan and repair.

# docker run -it --rm --privileged registry.opensuse.org/isv/rancher/harvester/toolbox/main/fs-toolbox:latest -- bash

Then we try to scan with this target device.

XFS​

When scanning an XFS filesystem, use the xfs_repair command and specify the problematic partition of the device.

In the following example, /dev/sda3 is the problematic partition.

# xfs_repair -n /dev/sda3

To repair the corrupted partition, run the following command.

# xfs_repair /dev/sda3

EXT4​

When scanning a EXT4 filesystem, use the e2fsck command as follows, where the /dev/sde1 is the problematic partition of the device.

# e2fsck -f /dev/sde1

To repair the corrupted partition, run the following command.

# e2fsck -fp /dev/sde1

After using the 'e2fsck' command, you should also see logs related to scanning and repairing the partition. Scanning and repairing the corrupted partition is successful if there are no errors in these logs.

Detach and Start VM again.​

After the corrupted partition is scanned and repaired, detach the volume and try to start the related VM again.

• Detach the volume from the Longhorn UI.

• Start the related VM again from the Harvester UI.

Your VM should now work normally.

Harvester replicates volumes data across disks in a cluster. Before removing a disk, the user needs to evict replicas on the disk to other disks to preserve the volumes' configured availability. For more information about eviction in Longhorn, please check Evicting Replicas on Disabled Disks or Nodes.

Preparation​

This document describes how to evict Longhorn disks using the kubectl command. Before that, users must ensure the environment is set up correctly. There are two recommended ways to do this:

1. Log in to any management node and switch to root (sudo -i).
2. Download Kubeconfig file and use it locally
   • Install kubectl and yq program manually.
   • Open Harvester GUI, click support at the bottom left of the page and click Download KubeConfig to download the Kubeconfig file.
   • Set the Kubeconfig file's path to KUBECONFIG environment variable. For example, export KUBECONFIG=/path/to/kubeconfig.

Evicting replicas from a disk​

1. List Longhorn nodes (names are identical to Kubernetes nodes):

   kubectl get -n longhorn-system nodes.longhorn.io
   

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   Sample output:

   NAME    READY   ALLOWSCHEDULING   SCHEDULABLE   AGE
   node1   True    true              True          24d
   node2   True    true              True          24d
   node3   True    true              True          24d
   

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2. List disks on a node. Assume we want to evict replicas of a disk on node1:

   kubectl get -n longhorn-system nodes.longhorn.io node1 -o yaml | yq e '.spec.disks'
   

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   Sample output:

   default-disk-ed7af10f5b8356be:
     allowScheduling: true
     evictionRequested: false
     path: /var/lib/harvester/defaultdisk
     storageReserved: 36900254515
     tags: []
   

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3. Assume disk default-disk-ed7af10f5b8356be is the target we want to evict replicas out of.

   Edit the node:

   kubectl edit -n longhorn-system nodes.longhorn.io node1 
   

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   Update these two fields and save:

   • spec.disks.<disk_name>.allowScheduling to false
   • spec.disks.<disk_name>.evictionRequested to true

   Sample editing:

   default-disk-ed7af10f5b8356be:
     allowScheduling: false
     evictionRequested: true
     path: /var/lib/harvester/defaultdisk
     storageReserved: 36900254515
     tags: []
   

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4. Wait for all replicas on the disk to be evicted.

   Get current scheduled replicas on the disk:

   kubectl get -n longhorn-system nodes.longhorn.io node1 -o yaml | yq e '.status.diskStatus.default-disk-ed7af10f5b8356be.scheduledReplica'
   

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   Sample output:

   pvc-86d3d212-d674-4c64-b69b-4a2eb1df2272-r-7b422db7: 5368709120
   pvc-b06f0b09-f30c-4936-8a2a-425b993dd6cb-r-bb0fa6b3: 2147483648
   pvc-b844bcc6-3b06-4367-a136-3909251cb560-r-08d1ab3c: 53687091200
   pvc-ea6e0dff-f446-4a38-916a-b3bea522f51c-r-193ca5c6: 10737418240
   

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   Run the command repeatedly, and the output should eventually become an empty map:

   {}
   

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   This means Longhorn evicts replicas on the disk to other disks.

   note

   If a replica always stays in a disk, please open the Longhorn GUI and check if there is free space on other disks.