This is documentation for MapR Version 5.0. You can also refer to MapR documentation for the latest release.

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MapR-FS groups disks into storage pools, usually made up of two or three disks. When adding disks to MapR-FS, it is a good idea to add at least two or three at a time so that MapR can create properly-sized storage pools. Each node in a MapR cluster can support up to 36 storage pools.

To see which disks are used by MapR-FS, check the disktab file that MapR maintains on each node.

The following sections provide procedures for working with disks:

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For instructions on performing disk maintenance on a node, see Performing Maintenance on a Node. If a disk failure alarm is raised (NODE_ALARM_DISK_FAILURE), see Handling Disk Failures for instructions.

Adding Disks

You can add one or more available disks to MapR-FS using the disk add command or the MapR Control System. In both cases, MapR automatically takes care of formatting the disks and creating storage pools.

To add disks using the MapR Control System:

  1. Add physical disks to the node or nodes according to the correct hardware procedure.
  2. In the Navigation pane, expand the Cluster group and click the Nodes view.
  3. Click the name of the node on which you wish to add disks.
  4. In the MapR-FS and Available Disks pane, select the checkboxes beside the disks you wish to add.
  5. Click Add Disks to MapR-FS to add the disks. Properly-sized storage pools are allocated automatically.

Removing Disks

You can remove one or more disks from MapR-FS using the disk remove command or the MapR Control System. When you remove a disk from MapR-FS, any other disks in the storage pool are also removed automatically from MapR-FS and are no longer in use (they are available but off-line). Their disk storage goes to 0%, and they are eligible to be re-added to MapR-FS to build a new storage pool. You can either replace the disk and re-add it along with the other disks that were in the storage pool, or just re-add the other disks if you do not plan to replace the disk you removed.

  • If you are removing and replacing failed disks, you can install the replacements, then re-add the replacement disks to MapR-FS, along with the other disks that were in the same storage pool(s) as the failed disks. See Handling Disk Failures for more details.
  • If you are removing disks but not replacing them, you can just re-add the other disks that were in the same storage pool(s) as the failed disks.
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Before removing or replacing disks, make sure the Replication Alarm (VOLUME_ALARM_DATA_UNDER_REPLICATED) and Data Alarm (VOLUME_ALARM_DATA_UNAVAILABLE) are not raised. These alarms can indicate potential or actual data loss! If either alarm is raised, you might be able to repair the problem using the /opt/mapr/server/fsck utility before removing or replacing disks.

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Using the /opt/mapr/server/fsck utility with the -r flag to repair a filesystem risks data loss. Call MapR support before using /opt/mapr/server/fsck -r.

To remove disks using the MapR Control System:

  1. In the Navigation pane, expand the Cluster group and click the Nodes view.
  2. Click the name of the node from which you wish to remove disks.
  3. In the MapR-FS and Available Disks pane, select the checkboxes beside the disks you wish to remove.
  4. Click Remove Disks from MapR-FS to remove the disks from MapR-FS.
  5. Wait several minutes while the removal process completes. After you remove the disks, any other disks in the same storage pools are taken offline and marked as available (not in use by MapR).
  6. Remove the physical disks from the node or nodes according to the correct hardware procedure.

Tolerating Slow Disks

The parameter mfs.io.disk.timeout in mfs.conf determines how long MapR waits for a disk to respond before assuming it has failed. If healthy disks are too slow, and are erroneously marked as failed, you can increase the value of this parameter.

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