How does Windows 2008 remember drive letter / mount point associations

disk-imagestoragewindows-server-2008-r2

We use storage array features to clone LUNs and then map these "new" LUNs out again to the same or different hosts. A typical case is when we refresh between environments, so imagine cloning a LUN holding a bunch of VMs from source host TEST1 to destination host TEST2. Sometimes the destination host will assign the drive automatically, and sometimes it won't. The storage array changes the cloned LUN's serial number (but we could modify it back) but for the rest the cloned LUN contents are identical to the source. In the case of a refresh (so in this example remove the old LUN from TEST2 and then map the cloned LUN in it's place) the LUN ID also stays the same. The LUNs are accessed over a Fibre Channel SAN and are thus not seen as removable devices. Needless to say, in the situation here we are not cloning the boot LUN itself either.

I found Microsoft KB234048 describing the behavour with Windows 2000 but I suspect a lot has changed in the last 10 years.

If anyone has details, including special cases like if they are MSCS shared disks, or multiple disks with matching signatures (i.e.cloned disk is maped to same server), please share!

Best Answer

Well, actually not much has changed - the associations are still stored in the registry within the HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices key. Some insight about what to put in there / how to interpret the data comes from this 3rd party docs.

Related Solutions

Linux – Fibre Channel LUN rescan and QLogic

In the off chance that the block device is being detected, but no /dev/ device is being created, you can manually create the device. This isn't optimal, but might limp you along. The major and minor numbers are presented in /proc/partitions, and you can create your own block devices through the mknod command.

 # mknod /dev/sdg4 104 17

However, I feel your pain. QLogic offers driver download for RHEL and SUSE but it seems no other distros. OpenSUSE just might have the QLogic-branded drivers but I can't be certain of it. I'll check closer when I get to work.

Edit: I'm at work, and it does seem that the QLogic drivers on my SLES boxes are all the QLogic supplied one. Their OS support grid:

http://filedownloads.qlogic.com/files/Driver/71098/readme_driver_80223.html#os_support

And yet, when I download the bog-standard 2.6.27.25 kernel and look in the ./drivers/scsi/qla2xxx/qla_version.h file it is nearly the same version numbers as I have on my Novell distros (both SLES, and the free openSUSE). Which suggests that the solution you found for SLES/RHEL may actually work with a standard 2.6.27.25 kernel.

Windows 2000 Fibre LUN Rescan Doesn’t See New Increased Capacity

I am pretty sure this is a kinown issue with Windows Server 2000. It didn't support disks that changed size without a dismount/remount. We hit this issue a number of times. Typically the way you solve this is with thin provisioining/storage virtualization. I.e. you create a partition that says it is 2TB but is only backed by 500GB of storage. Then behind the scenes you can add storage over time either manually or autoamtically up to the 2TB limit without requiring a reboot. Once you go beyond that you will have to reboot the system.

Worked for us back when this was an issue. Alternative is to upgrade the OS. I seem to remember Server 2003 deals with this much better.

Thanks,

Chris

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