Online Relayout

Storage Layout

Online Relayout currently supports these storage layouts:

How Online Relayout Works

The VERITAS Online Relayout feature allows you to change storage layouts that you have already created in place, without disturbing data access. You can change the performance characteristics of a particular layout to suit changed requirements.

For example, if a striped layout with a 128K stripe unit size is not providing optimal performance, change the stripe unit size of the layout by using the Relayout feature. You can transform one layout to another by invoking a single command.

File systems mounted on the volumes do not need to be unmounted to achieve this transformation as long as the file system provides online shrink and grow operations.

Online Relayout reuses the existing storage space and has space allocation policies to address the needs of the new layout. The layout transformation process converts a given volume to the destination layout by using minimal temporary space.

The transformation is done by moving a portion-at-a-time of data in the source layout to the destination layout. Data is copied from the source volume to the temporary space, which removes data from the source volume storage area in portions. The source volume storage area is then transformed to the new layout and data saved in the temporary space is written back to the new layout. This operation is repeated until all the storage and data in the source volume has been transformed to the new layout.

You can use Online Relayout to change the number of columns, change stripe width, remove and add parity, and change RAID-5 to mirroring.

Types of Transformation

At least one of the following criteria must be met for an Online Relayout operation to be effective. You must perform one or more of the following operations:

To be eligible for layout transformation, mirrored volume plexes must be identical in layout, with the same stripe width and number of columns. See Table 3-1 “Supported Layout Transformations”

Entries in Table 3-1 “Supported Layout Transformations” include the following:

Number Descriptions

The numbers in Table 3-1 “Supported Layout Transformations” describe the Relayout operation as follows:

1. Changes the stripe width or number of columns.

2. Removes all of the columns.

3. Not a Relayout, but a convert operation.

4. Changes mirroring to RAID-5 and/or stripe width/column changes.

5. Changes mirroring to RAID-5 and/or stripe width/column changes.

6. Changes stripe width/column and remove a mirror.

7. Adds columns.

8. Not a Relayout operation.

9. A convert operation.

10. Changes mirroring to RAID-5. See the vxconvert procedure.

11. Removes a mirror; not a Relayout operation.

12. Removes a mirror and add striping.

13. Changes an old mirrored volume to a stripe mirror. Relayout is valid only if there are changes to columns/stripe width; otherwise, this is a convert operation. See the vxconvert procedure.

14. Changes an old mirrored volume to a concatenated mirror. Relayout is valid only if there are changes to columns; otherwise, this is a convert operation.

15. No changes; not a Relayout operation.

16. Changes an old mirrored volume to RAID-5. Choose a plex in the old mirrored volume to use Relayout. The other plex is removed at the end of the Relayout operation.

17. Unless you choose a plex in the mirrored volume and change the column/stripe width, this is not a Relayout operation.

18. Unless you choose a plex in the mirrored volume and change the column/stripe width, this is not a Relayout operation.

19. Not a Relayout operation.

20. Changes stripe width/column.

21. Removes parity and all columns.

22. Removes parity.

23. No changes; not a Relayout operation.

24. Removes columns.

25. Changes stripe width/number of columns.

A striped mirror plex is a striped plex on top of a mirrored volume, resulting in a single plex that has both mirroring and striping. This combination forms a plex called a striped-mirror plex. A concatenated plex can be created in the same way. Online Relayout supports transformations to and from striped-mirror and concatenated-mirror plexes.

	NOTE: Changing the number of mirrors during a transformation is not currently supported.

Transformation Characteristics

Transformation of data from one layout to another involves rearrangement of data in the existing layout to the new layout.

During the transformation, Online Relayout retains data redundancy by mirroring any temporary space used.

Read/write access to data is not interrupted during the transformation.

Data is not corrupted if the system fails during a transformation. The transformation continues after the system is restored and read/write access is maintained.

You can reverse the layout transformation process at any time, but the data may not be returned to the exact previous storage location. Any existing transformation in the volume should be stopped before doing a reversal.

You can determine the transformation direction by using the vxrelayout status command.

These transformations eliminate I/O failures as long as there is sufficient redundancy to move the data.

Transformations and Volume Length

Some layout transformations can cause the volume length to increase or decrease. If the layout transformation causes the volume length to increase or decrease, Online Relayout uses the vxresize command to shrink or grow a file system.

Sparse plexes are not transformed by Online Relayout, and no plex can be rendered sparse by Online Relayout.

	NOTE: Online Relayout can be used only with volumes created with the vxassist command.

Transformations Not Supported

Transformation of log plexes is not supported.

A snapshot of a volume when there is an Online Relayout operation running in the volume is not supported.