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I had low disk space problem in windows 7 installation. And there was no way to increase the volume size of my C: drive. So I first backup the disks unix cat command.

cat /dev/sdb1 > /media/tape8/sdb1_windows7.img

Then I repartitioned my hard disk. Give enough space (30GB) to windows drive (C:). After that I restore the image to the new 30GB partition by

cat /media/tape8/sdb1_windows7.img > /dev/sdb1

Now I try to boot windows. It doesn't boot. I try to repair by windows 7 installation disk. Tried Startup Repair, nothing changes.

My question is, on this scenario how do I boot my existing windows?

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That is quite an unusual way to back up a disk - dd might have worked better, or to use some bootable disk repartitioning tool. – Journeyman Geek Dec 17 '11 at 9:57
Yeah, DD was better. But dd is way too slow. and selecting optimal bsize is the key here. But I could find the proper size. I did the cat. – Shiplu Dec 17 '11 at 12:28
up vote 2 down vote accepted

What I would try:

Shrink the partition back to original size (i hope you backed up your partition table) and put the data back. Hopefully this will boot. In Windows and use diskmgmt.msc to extend the volume to the free space ...

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