Configure a software raid 1 mirroring in windows 7

You need to use a HDD as big or bigger then the one you want to mirror, one identical would be best.

Open Disk Management either by accessing Computer Management by Right click - on My Computer - and select Manage - then select under Storage - Disk Management
or type in Run - diskmgmt.msc

IF you want to make a mirror to your active windows hdd you MUST start first with the System Reserved partition (100MB NTFS) or convert the whole hdd to dynamic first.
(if you start mirroring from the second, third etc partition you will not be able to mirror the System Reserved partition unless you wipe the hole hdd and reinstall windows)

Right click System Reserved partition and select Mirror volume - select the empty disk press OK and then you will be asked if you want to convert the two HDD to dynamic disks.
Select OK.
Wait for each mirrored partition to sync or it will take many hours to sync them in parallel

This will only work with MBR formated HDD - and for booting/installing Windows you must select in BIOS - boot options Legacy Mode (not UEFI).
If you chose to install windows with GPT partitioning style it will create some system reserved partitions that are not visible in disk management so you will be unable to mirror them.

RAID 0 - stripping for performance
RAID 1 - MIRRORING
RAID 10 - https://www.youtube.com/watch?v=bcCfVYZa0k0