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Old 11-21-2008, 04:47 AM   #1
banz
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Registered: Aug 2004
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Using dd and gzip to create hard drive image but image is bigger than hard drive?


What we are trying to accomplish is to migrate 20 windows 2000 machines to new hardware and also to take an image of the machine on the old hardware and the new hardware.

We are using an unbuntu live CD to boot up the machine. The hard drive itself is about 4gb. Using the commands

dd if=/dev/sda | gzip > /mnt/landesk/f$/images/image.gz

This gzip compress it from 4gb to 1.2gb. We then restore this image to the new hardware using

gzip -dc /mnt/landesk/f$/images/image.gz | dd of=/dev/sda

It seems to work but due to the difference in hardware we have to run the windows repair to get it to work. It adds about 300mb to the total size of the disk.

We run df -h and it shows it's only used 4.8gb

bt ~ # df -h
Filesystem Size Used Avail Use% Mounted on
aufs 447M 7.8M 439M 2% /
/dev/sda1 38G 4.8G 33G 13% /mnt/sda1
//landesk2/f$ 1.3T 264G 1006G 21% /mnt/pcd


So now we need to take a new image of the working hardware using the same command
dd if=/dev/sda | gzip > /mnt/landesk/f$/images/image.gz
This time gzip gives us an error saying that the file size has exceeded. So we decided to split the file using

dd if=/dev/sda | gzip -c9 | split -b 2000m - /mnt/landesk/f$/images/image.gz

This completes with

78165360+0 records in
78165360+0 records out
40020664320 bytes (40 GB) copied, 9205.89 s, 4.3 MB/s

The total size of the image is about 11.5gb! Any idea why the size of the image is bigger than the hard drive? There isn't any other partition on the hard drive.
 
Old 11-21-2008, 09:52 PM   #2
billymayday
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Registered: Mar 2006
Location: Sydney, Australia
Distribution: Fedora, CentOS, OpenSuse, Slack, Gentoo, Debian, Arch, PCBSD
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I'm missing something - isn't the drive 40G?
Code:
40020664320 bytes (40 GB) copied, 9205.89 s, 4.3 MB/s
What does fdisk -l show?

Did you mean to do
Code:
dd if=/dev/sda1 | gzip -c9 | split -b 2000m - /mnt/landesk/f$/images/image.gz
?

Last edited by billymayday; 11-21-2008 at 09:55 PM.
 
Old 11-22-2008, 03:07 AM   #3
banz
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Registered: Aug 2004
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Thanks for your reply billymayday. The drive is 40gb, but only 4.8gb in data. So I thought when you gzip it, it should be less than 4gb in size?

Can't do fdisk -l at the moment as I'm not in at work today.

I used dd if=/dev/sda because it also takes an image of the MBR.

Correct me if I'm wrong, I have a feeling that the size of the image is big is because the drive is not clean? I didn't really wipe the drive before restoring the image on to the hard drive.

After writing 0 to the drive, restoring the image, reimaging the drive again. The size seems to be right again! It's only 1.3gb after gzip.

I'm going to have to do more testing when I get into work in Monday.
 
Old 11-22-2008, 04:25 AM   #4
billymayday
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Registered: Mar 2006
Location: Sydney, Australia
Distribution: Fedora, CentOS, OpenSuse, Slack, Gentoo, Debian, Arch, PCBSD
Posts: 6,678

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I'd guess that is right. if the drive was all zeros, and only 4.8G, I think you'd be correct. it probably isn't.
 
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