How to create a program which is working similar like RAID1 (mirroring)?

I want to create a simple program which is working very similar to RAID1. It should work like this:

First i want to give the primary HDD-s drive letter and than the secondary one. I will only write to the primary HDD! If any new data is copied to the primary HDD it should automatically copy it to the secondary one.

I need some help where should i start all this? How to monitor the written data in the primary HDD? Obviously there are many ways to do what i want (i think), but i need the simpliest way.

If this isn't so complicated, than how can i handle that case if the primary HDD has two or more partition, because then i should check the secondary HDD's partition too, and then create/resize them if necessary?

Thanks in adv开发者_运维知识库ance!

kampi

The concept of mirroring disk writes to another disk in real time is the basis for high availability, and implementing these schemes are not trivial.

The company I work for makes DoubleTake, which does real time mirroring & replication of file based IO to local or remote volumes. This is a little different than what you are describing, which appears to be block based disk/volume replication, but many of the concepts are similar.

For file based replication, there are a quite a few nasty scenarios, i'll describe a few:

1. Synchronizing the contents of one volume to another volume, keeping in mind that changes can occur while you are doing this. I suppose you could simply this by requiring that volumes start out totally formatted. But for people that have data that will not be a good solution!

2. keeping up with disk changes: What if the volume you are mirroring to is slower than the source volume? Where do you buffer? To Disk? Memory?

Anyways we use a kernel mode file system filter driver to capture the disk IO, and then our user mode service grabs this IO and forwards it to a local or remote disk.

If you want to learn about file system filtering, one of the best books (its old but good) is File System Internals, by Rajeev Nagar. Its a must read for doing any serious work with file system filters.

Also take a look at the file system filter samples on the Windows 7 WDK, its free, and they have good file mon examples that will get you seeing disk changes pretty quickly.

Good Luck!