Moving dynamic disks to a new Windows server

It's a simple enough process to migrate dynamic disks into another Windows system as long as you take certain factors into account to avoid data loss.

Last summer, lightning literally destroyed one of my servers. Although the server itself was ruined, I suspected that the server's disks might still be good. As such, I purchased a new server and installed the Windows operating system on it.

My plan was to move the data volumes from my old server into my new one. To make a long story short, the procedure worked as intended. If you find yourself in a similar situation, though, you may be in for some surprises if the disks you're moving are configured to act as dynamic disks.

Let's take a look at how to move dynamic disks from one server to another without losing data in the process.

The first thing that you need to understand about moving dynamic disks is that Windows treats them as if they belong to a disk group. This is important because Windows only supports one disk group per server. Therefore, if you simply install the dynamic disks into the new machine, Windows will not immediately allow you to access those disks because they belong to a foreign disk group. Fortunately, Microsoft gives us a simple way to import foreign disks into a disk group.

Preventing data loss

Before I show you how to actually move the disks, it's important to first learn how to avoid data loss. The reason why Windows treats all dynamic disks as if they belong to a group is because Windows handles all dynamic disks in the system as contributing to a pool of disk space. Most admins know that they can create volumes that span multiple dynamic disks. Windows also allows you to create RAID volumes at the software level. Herein lies the problem.

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If the system that originally contained the disks only has one disk configured as being dynamic, then there really isn't much consideration involved in moving it. The same principle applies if the server that originally contained the dynamic disks was set up in such a way that no volume spans multiple disks. If a volume spans multiple disks, or if you are using a RAID implementation (at the software level), then you have to do some additional planning.

Generally speaking, in order to avoid data loss, you have to move all of the disks that comprise the volume. There are a couple of exceptions to this, though. For example, if the disks you want to move are part of a mirror set, you can break the mirror and then move only half of the set.

Note: Technically, you can move half of the mirror set without first breaking the mirror. However, if you do this and eventually decide to move the other half of the mirror set, the server will experience problems because the two sets are out of sync.

It's also possible to move all but one of the disks in a RAID 5 set without losing any data. As you probably know, RAID 5 places parity information on each disk so that it can function -- even if one of the disks in the site goes bad. Even so, I recommend moving all of the disks in the set if possible, because moving a partial RAID 5 set impacts performance unless you add another disk to the set later on.

There is one last thing to keep in mind before moving the dynamic disks. If the server that originally contained the disks is still functional, it's a good idea to open the Disk Management console and verify that the volumes you are moving are healthy. If the console reports any problems with the volumes, then you will need to fix them prior to moving the disks.

Transplanting the disks

With that said, you can then go ahead and move the disks into the new computer, boot the server and open the Disk Management console. The console should display the newly transplanted disks as Dynamic/Foreign.

First, verify that the disks you have just transplanted are listed as being online. If not, you should be able to bring them online by right-clicking on the volume and choosing the Online option from the resulting shortcut menu.

You can then import the foreign disks. To do so, right-click on the disk and choose the Import Foreign Disks option from the resulting shortcut menu. If the new system did not previously contain any dynamic disks, then the disks are imported as they are and the new system basically just adopts them. If the new system already contains dynamic disks, then the imported disks merge into the existing disk group. From the administrator's perspective, though, this difference is trivial.

ABOUT THE AUTHOR
Brien M. Posey, MCSE, has received Microsoft's Most Valuable Professional Award four times for his work with Windows Server, IIS and Exchange Server. He has served as CIO for a nationwide chain of hospitals and healthcare facilities, and was once a network administrator for Fort Knox. You can visit his personal Web site at www.brienposey.com.

This was first published in August 2008

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