mdadm grow fails with "mdadm: Cannot add bitmap while array is resyncing or reshaping etc."

When managing your RAID arrays on Linux, you may encounter an error message that says "mdadm: Cannot add bitmap while array is resyncing or reshaping etc." This error typically occurs when you try to grow or modify your RAID array while it is still in the process of resyncing or reshaping. In this article, we will explain what this error means, why it occurs, and how you can resolve it.

Understanding RAID and mdadm

RAID (Redundant Array of Independent Disks) is a technology that allows you to combine multiple physical disks into a single logical unit for better performance, reliability, or both. Linux provides a software utility called mdadm (Multiple Device Administrator) to manage RAID arrays.

Resyncing and Reshaping

When you create or modify a RAID array, mdadm needs to synchronize the data across all the disks involved. This process is known as resyncing. Resyncing ensures that the data is consistent on all disks and that the array is ready for use.

Reshaping, on the other hand, refers to changing the configuration of an existing RAID array, such as adding or removing disks. Reshaping involves both resyncing and redistributing the data across the new configuration.

The "mdadm: Cannot add bitmap" Error

While your RAID array is undergoing resyncing or reshaping, mdadm temporarily disables certain operations to prevent data inconsistencies. One of these disabled operations is adding a bitmap to the array.

A bitmap is a data structure that tracks the changes made to the array during resyncing or reshaping. It helps mdadm to resume the process from where it left off in case of an interruption.

When you attempt to add a bitmap to a RAID array that is still resyncing or reshaping, mdadm throws the "mdadm: Cannot add bitmap while array is resyncing or reshaping etc." error to prevent any potential conflicts or data corruption.

Resolving the Error

To resolve the "mdadm: Cannot add bitmap" error, you need to wait until the resyncing or reshaping process is complete before adding the bitmap to your RAID array. You can monitor the progress of the process by using the following command:

Replace /dev/mdX with the actual device name of your RAID array. Look for the "State" field in the output. If it shows "resyncing" or "reshaping," you need to wait until it changes to "clean" or "active" before proceeding.

Once the resyncing or reshaping is complete, you can add the bitmap to your RAID array using the following command:

Replace /dev/mdX with the actual device name of your RAID array. The --bitmap=internal option specifies that the bitmap should be stored internally within the array.

After adding the bitmap, you can verify its presence by running the following command:

If everything is successful, you should see a line that says "Bitmap : Internal"

The "mdadm: Cannot add bitmap while array is resyncing or reshaping etc." error occurs when you try to add a bitmap to a RAID array that is still in the process of resyncing or reshaping. To resolve this error, you need to wait until the process is complete and then add the bitmap using the appropriate mdadm command. Remember to monitor the progress using the --detail option to ensure that the array is in a suitable state for modification.

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