Knowledge Document: How to prevent deleted data on excluded logical volumes (LV) to be recognize by PlateSpin Migrate

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Environment

PlateSpin Migrate 2020.8
PlateSpin Migrate 2020.5

Situation

A situation in which PlateSpin recognized some data deletion on the excluded logical volumes, resulting in fragmentation and causing an inflated migration size.
 

Resolution

NOTE: Make sure to always take proper backups of your data before performing any disk-related operations to ensure data safety in case of unexpected issues.

Some possible approach to prevent inflated migration size.

1.Defragmentation: Before initiating the migration, perform defragmentation on the logical volumes that will be migrated. This will help consolidate the data and reduce the chances of PlateSpin interpreting deleted data as used space.


A. To do this, first ensure that the filesystem to be defragmented is ext4. To do this you can use 'lsblk -f' or 'df -T' to display the filesystem type.

B. Unmount the Filesystem: unmount the filesystem before performing defragmentation. Make sure the filesystem is not in use before proceeding.

C. Run the Defragmentation Command:

Use the e4defrag command to defragment the ext4 filesystem. Replace /dev/<your-filesystem> with the actual path of the filesystem you want to defragment.

#sudo e4defrag /dev/<your-filesystem>


D. Remount the Filesystem:

After the defragmentation has completed, you can remount the filesystem:

#sudo mount /dev/<your-filesystem> /mount/point


2. Zero-Fill or Shrink Excluded LVs: If specific LVs are to be excluded and their data is no longer required, the customer can consider zero-filling or shrinking these LVs before migration. Zero-filling involves writing zeros to the unused space within the LV, indicating to the migration tool that the data is not in use. Shrinking the LVs will reclaim the space as free space before the migration, reducing the overall migration size.

To do this, first, ensure that the LV you want to zero-fill is unmounted and not in use.

Use the dd command to write zeros to the unused space within the LV. Replace /dev/<your-lv> with the actual path to the LV you want to zero-fill.
 

#sudo dd if=/dev/zero of=/dev/<your-lv> bs=1M status=progress

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