On 23 Nov 2020 at 12:50, Samuel Sieb wrote:
Subject: Re: Clone logical volume using dd
To: users(a)lists.fedoraproject.org
From: Samuel Sieb <samuel(a)sieb.net>
Date sent: Mon, 23 Nov 2020 12:50:46 -0800
Send reply to: Community support for Fedora users
<users(a)lists.fedoraproject.org>
On 11/23/20 1:02 AM, Michael D. Setzer II via users wrote:
> dd bs=1M if=$localback |lzop -c - > /mnt/local$localpath$localimagename
>
> I use lzop for compression of image, since it gives good compress and is
> considerable faster than gzip.
>
> Note: Since it does copy all blocks, it is best to clear the currently
> unused blocks before hand. Long ago, did an image of a disk with clean
> install of Fedora 3 on 80GB disk. Image created was 12G in size
> compress. Cleared free space, and redid imaged, and size dropped to
> 2.5G. Compression does depend on what is on disk..
This is still not suitable for his purpose. It's not about the
compressed size, it's about the number of blocks copied. Using dd, you
are still copying *all* the unused blocks which will be really bad for a
thin LV which is the intended destination.
The difference between a bit level image and an image that has to
understand all aspects of the partition info. If the unused data blocks are
cleared by filling with nulls, it compress to nothing. The resulting images
are very similar in size.
Agree, it takes longer to make the image, since it does have to read all
blocks of the disk/partition, but it copies all data. Using a program that
determines what needs to be backed up and what doesn't may or may not
copy everything at some point.
With the disk bit level images, one could restore to a new disk, and not
have to do any prep of creating the partition setup, since that was already
included in the image. With partitions, that isn't an issue.
I had linux and windows on my classroom machines, and sometimes
imaged one system to all the other machines using udpcast with bit level
image. Also, had options to be able to restore the windows image in
about 10 minutes to its partition from the local extra partition.
So, just another option.
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+------------------------------------------------------------+
Michael D. Setzer II - Computer Science Instructor (Retired)
mailto:mikes@guam.net
mailto:msetzerii@gmail.com
Guam - Where America's Day Begins
G4L Disk Imaging Project maintainer
http://sourceforge.net/projects/g4l/
+------------------------------------------------------------+