So I've put on a bit of weight over the last few years and when I talk about thick to thin in a storage context I wish I could apply a thin migration plan to myself but alas the only solution for that is exercise which I don't do enough of at the moment!
Anyhow - migrating to thin pools is something that comes up in discussion on a regular basis and over the last few months I've been privileged enough to author migration plans for and use in anger most of the great tools that EMC have to ensure customers get the very best out of that minuscule 768KB sub-extent size utilized by the Symmetrix VMAX!
Typical migrations usually consist of loads of traditionally provisioned storage arrays that are being consolidated into a new EMC Symmetrix VMAX which in most environments these days is being configured with VP pools were customers are leveraging other technologies such as Virtual-LUN and FAST VP or just simply VP itself.
For those who intend to or are leveraging virtual provisioning pool over-subscription the chances are that you're going to want to strip out the unused zeroes during any inbound data migration......and EMC provide a range of array and host level tools to facilitate this objective.
Array-based migrations to thin pools
On the VMAX itself there are currently two migration methods that you can use to strip out those unwanted zeroes and the products that facilitate this are SRDF and Open Replicator. For those of you who have been around Symms these products have been available for years and are probably the most tried and tested replication products in the enterprise storage market and in VMAX the developers have added the ability to reclaim zeroed space in flight with a few caveats. With SRDF, you must currently use adaptive copy mode and with Open Replicator the control volumes must exist on the Symmetrix VMAX and these methods are the perfect fit for migration purposes.
Host-based Migrations to thin pools
If your migration plan can't leverage an array based method then you're going to ask the host to move the data, which is not ideal as the array should do this for you but is sometimes a necessity for one reason or another. EMC have the tools in this space to help and these are currently Open Migrator/LM and PowerPath Migration Enabler (Host Copy).
Open Migrator/LM is a very powerful product that in its simplest form copies an existing volume to a new VMAX volume and once in sync you choose a time to swap the target device over to be the new source - simple as that. If you are migrating Windows Server 2003 or 2008 machines to your new VMAX and need to correct partition alignment and/or NTFS cluster size then this product can do both - with the applications online.
PowerPath Migration Enabler (Host Copy) is a great feature of PowerPath. Assuming you've PowerPath patched to supported levels you can leverage PowerPath to facilitate an online migration for any device managed by PowerPath irrespective of whether its a LUN from an HP, IBM, EMC or any supported array.
If your migration plan can't leverage an array based method then you're going to ask the host to move the data, which is not ideal as the array should do this for you but is sometimes a necessity for one reason or another. EMC have the tools in this space to help and these are currently Open Migrator/LM and PowerPath Migration Enabler (Host Copy).
Open Migrator/LM is a very powerful product that in its simplest form copies an existing volume to a new VMAX volume and once in sync you choose a time to swap the target device over to be the new source - simple as that. If you are migrating Windows Server 2003 or 2008 machines to your new VMAX and need to correct partition alignment and/or NTFS cluster size then this product can do both - with the applications online.
PowerPath Migration Enabler (Host Copy) is a great feature of PowerPath. Assuming you've PowerPath patched to supported levels you can leverage PowerPath to facilitate an online migration for any device managed by PowerPath irrespective of whether its a LUN from an HP, IBM, EMC or any supported array.
It's also worth noting that many third party vendors at this point including VMware and Symantec support thin reclamation initiatives and recent versions of Storage Foundations and ESXi support various thin-aware features like SmartMove and Storage vMotion that can remove unsed zeros during migrations.
Conclusion
Some of the benefits behind reclaiming contiguous zeroes in flight during a migration are that it minimizes capacity consumption and reduces the load on the array as only extents with data are actually being written to disk. All in all these migration methods can be used to reduce or eliminate the downtime usually associated with such migration activities and reclaim valuable unused capacity.
Those who can't take advantage of these thin friendly migration tools to Symmetrix VMAX you do have the option to run an online Zero Space Reclaim (ZSR) post traditional migration methods which releases blocks of contiguous unused extents back into the pool for reuse.
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