When migrating data from an old array to a new one, there are many tools to help. EMC VMAX provides a built-in tool called Open Replicator for Symmetrix (ORS), which can push and pull data to and from other arrays. This is a quick review of the benefits one customer has seen using ORS.
Moving Data
ORS makes the VMAX host ports look like a Windows server to other arrays in the SAN (EMC or not). The VMAX needs to be granted zoning access to the original devices on the source array.
Once the VMAX has proper access, the data can be pulled into new devices. The new VMAX devices are usually Virtually Provisioned (thin) devices, as VP devices are much simpler to manage both for capacity and performance reasons.
Recovering Space
As a part of the migration, the VMAX can look for empty areas on the source device. Since VMAX VP volumes allocate space in 768k extents, any aligned 768k of data that is all zeros does not need to be saved on disk, since reads from unallocated space always report zeros. By activating the zero detection with ORS, these extents of all zero data are never written to disk. The use of this relatively small extent size allows for a much finer-grained recovery than some other systems.
Customer Example
I have a customer that has been using ORS for a
while to perform migrations. However, they were reluctant to use the zero
detection. There was a concern that this was somehow not compatible with all
operating systems (it is, always), or that it would otherwise present a risk to
their systems. They did some testing in the lab, and became comfortable with
the process. Then they tried it in production. Now they can’t get enough of
this technology.
Here are their results. For the next 25 servers that they migrated, there was 20.4TB of capacity on the LUNs they were moving. By using the ORS with zero detection, at the end of their move they had 11.7TB of data written on disk – and they had just saved over 8.8TB of capacity that had been all zeros. The graphic here shows the 3 largest systems (each over 2TB of source capacity) and the savings, as well as the overall results. In the end, they averaged over 43% savings by using the zero detection in their data migration.
There are many other options that can be used with ORS. For example, some systems need additional space as they grow, and the data migration can be a great time to add it. The ORS migration can be to new devices that are the same size or larger than the reported size of the source devices.
Also, when making production changes, customers want a backout plan. To make this simple, ORS has a “donor update” option. When active, all writes are synchronously written to the source array as well. This ensures that the original system always has a full copy of the production data.
And there is Federated Live Migration, the non-stop migration option for ORS. By using the –migrate option with supported systems, the migration can be completed without any downtime to production.
