Jeffrey Slapp

Migration with DataCore SANsymphony – Part 3

MIGRATION TYPE #2: ASYNCHRONOUS MIGRATION

Asynchronous migration refers to migrating the data between two systems that are greater than 100 km (62 mi) apart. In most scenarios, this would represent a migration between datacenters, cities or even countries. There is technically no distance limitation to this approach as long as you have a standard TCP/IP connection between the sites.

Just as before with the synchronous approach, we are going to start out with a LUN that has existing data on it (“Existing Storage LUN 0” on DCSSV01) and a LUN that will be used as the destination LUN (“New Storage LUN 0” on DCSSV02). This process can be accomplished from engines within the same group or across different groups.

In order to begin the process of migrating the data from the LUN connected to DCSSV01 to the LUN connected to DCSSV02, we must first create a DataCore Virtual Disk. Simply right-click on the Virtual Disks object in the tree under DCSSV01 and select Create Virtual Disks.

The Create Virtual Disk wizard should now be visible. Simply give the virtual disk a friendly name which denotes its purpose, select a disk type of Single, and set a size for the virtual disk to any non-zero value. The size of the disk will be automatically resized later based on the geometry of the source volume. Click Next to continue.

IMPORTANT NOTE: With the asynchronous approach, we will not be selecting a disk type of Mirrored. The disk type of Single will be used here instead.

The next screen is where you will designate the physical disk which is backing the virtual disk. Normally this would be a disk pool, however in this case since we are migrating an existing disk and its associated data blocks, we will need to select Pass-Through Disk in the dropdown box for the DCSSV01 engine.

The last screen is simply an acceptance screen. Verify that the storage source is correct.

You will also be reminded that size of the virtual disk will be adjusted to match the source volume.

IMPORTANT NOTE: You will need to do the exact same process on the destination engine (DCSSV02) for the destination volume (New Storage LUN 0). Once completed, both volumes will be designated as single pass-through volumes.

Now that both volumes on both engines are designated as pass-through volumes, we can proceed with setting up the replication process. Right-click on the Virtual Disk named “Existing Storage LUN 0 – Source” and select Replication -> Create Replication.

You will be presented with the replication wizard. Simply select the destination DataCore engine (DCSSV02) and the destination virtual Disk (New Storage LUN 0 – Destination) from the respective dropdown boxes. Finally, click Create to start the process.

You will reminded the destination volume will be overwritten with the data from the source volume and that the destination volume will not allow access during the process unless activated or split. For the purposes of migration, we will be splitting the volume when we are done.

When the process begins, a consistency check will be performed on the source volume.

Once the consistency check is completed, a full initialization will occur. This is equivalent of a full seeding of the data structures from the source volume to the destination volume.

Once the full initialization is complete, the volumes will remain in sync until a split occurs severing the source from the destination.

To remove SANsymphony once the migration is complete, stop I/O on the source side to ensure that no changes are occurring during the transition. Once I/O is stopped ensure that the data buffer is empty (as shown on the screen above). This will be depicted by the “Remaining Data” having a value of zero. Then you can proceed with splitting the replication simply by clicking on the Split Replication button in the toolbar at the top. Once split, both DataCore engines can be shutdown and the new volume(s) on the new storage system can be presented directly to the application server(s) on the destination side.


Read more on migration here or take a look at DataCore’s SANsymphony here!

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