The functionality to reduce the size of a LUN has been around for some time on storage systems such as the HP StorageWorks EVA, and using tools such as HP StorageWorks Command View EVA makes this task is extremely simple.
The challenge has always been to make sure that the underlying operation system capable of handling this reduction in size of the Logical Volume.
As we have already seen in the article ‘Using Volume Shrink with Database files (Part 1)’ SQL Server is capable of taking advantage of this technology, so in this in this article we will complete the picture and have a look at how this functionality can be used in tandem with the operating system to achieve practical space saving benefits.
The shrink function can be executed via Windows Disk Manager and by right clicking on the volume you wish to shrink. You will find now in Windows 2008 that there is a ‘Shrink Volume’ option.
If you select ‘yes’ to this option, you will be presented with a dialog box asking for the amount you wish to shrink the volume by which can be seen in figure 1.
Figure 1, Logical Volume shrink dialogue box
Be aware that you cannot shrink the volume beyond 50% of its original size.
The reason for this is be due to the way Windows, for reliability reasons, places a copy of the Master Boot Record (MBR) at the half way point the volume. It’s this second MBR that prevents the shrinking operation reducing the size below this point.
Now that the Logical Volume has been shrunk it is appropriate that the underlying storage system LUN be shrunk so as to realize the true benefit.
This can be achieved by using the HP StorageWorks Command View EVA by highlighting the LUN size and reducing the size of the number to the percentage of the volume which has been shrunk.
Be aware that if you reduce the size of the LUN beyond to the size of the reduced logical volume this could lead to destruction of data. The tool should give a warning to make you aware of this as you conduct the process.
To conduct this operation using Command View is extremely simple. Some might say a little too simple as to very easy to destroy data in the process. If you are looking for a more sophisticated tool to accomplish this task, HP StorageWorks Replication Solution Manager may be more appropriate.
The application manages all local and remote replication features across the full EVA array storage family. One of its abilities is to coordinate the shrinking operation between the OS and the Array with the aid of an agent. The agent provides the communication Windows and the RSM and assures that the reduction in size of the LUN does not result in the accidental loss of data.
It now seems all the elements in place to make the shrinking of a LUN an attractive proposition in many scenarios. HP StorageWorks Management Application, Windows 2008 and SQL Server when used together can now deliver a practical approach to saving space on you much valued storage systems.
Platform and application details
Operating System: Windows Server 2008 RC1
Additional Software: HP StorageWorks Command View EVA
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