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Thursday, March 09, 2006

When do you need to recover AD?

...hopefully never!
But just in case, I will describe something called Fast Recovery during the following days...

There are alternatives to tape backups such as lag sites, but I will not go into that but rather I will talk about how it is possible to use shadow copies instead. I find it interesting and in conjunction with tape backups it can be effective.

The reason way I found this interesting is because it is fast and use a mirroring process that doesn't affect the system performance much. So in order to understand this we need some information how the underlying services works. Not to get into bit-level discussion I will give an overview:

Volume Shadow Copy (I will call it VSC)
With VSC you can create point-in-time snapshots of a volume, the service itself coordinates with other applications like backup software for instance and storage hardware to enable app-aware data management and it also support backup of open files.

There are three components that are needed in order to make a full shadow copy:
1. Requestor, which is the utility that request the copy (or rather request for the creation)
2. Writer, this is the software (app-specific) that makes sure that the data is ready to be copied.
3. Provider, this component gives the functionality to make the copy. VSC can use 3rd party hardware provider if needed.

Virtual Disk Service (I will call it VDS)
To make it short, it provides volume management with a single Windows interface which is used to manage storage devices. It also provides APIs for ISVs and IHVs to create storage solutions. The service itself use two CLI utilities, Diskpart and Diskraid. The Diskpart command is used to control creation, deletion and extension of dynamic and basic disk partitions. Diskraid is used to configure hardware RAID, to be specific, it is used to create, extend, delete and unmask LUs (logical units) on SANs.

Well, it simply makes your VSC data available for use. It do this by unmasking the backups stored on SAN. This means that it makes them visible and change the status from read-only to read/write. It also mounts the volume on the server. The whole process is called transport and is a virtual process since the data is on the storage array.

That is all I have time for now, got to catch a flight. I will continue another day :)


Nick Gillott said...

"got to catch a flight"?

Got to miss one due to drinking beer and playing on a laptop you mean?


Jimmy Andersson [AD & Security MVP] said... know me all too well... :)