Just for info. I've maintained the g4l disk imaging project since 2004,
and the basic line it uses for doing a partition/disk image locally is.
(dd bs=1M if=$localback 2>/dev/null |jetcat-mod -f 5000 -p $readsize
2>$progout |lzop -c - >/mnt/local$localpath$localimagename) &
It boots from a cd or flash or from grub menu as an option and runs in
ram, so partitions are not mounted. Uses a dialog text interface.
The above information variables are gotten from dialog script.
This is the basic required parts to make image - The removed stuff is to
have a running dialog process screen that displays why the copy happens
in background. The /mnt/local points to a partition or disk other than the
one being imaged. The $localback would be the /dev/sda1 or similar
being backed up for partition 1.
dd bs=1M if=$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..
use bs=1M did some testing, and found using bigger sizes made little or no
difference. Too small would make it slower..
Use to use it in my classroom all the time to back and reimage systems, but retired in
2017 with 36+ years teaching computer science at College..
Well, good luck and be Safe.
On 23 Nov 2020 at 9:12, Roberto Ragusa wrote:
Subject: Re: Clone logical volume using dd
To: users@xxxxxxxxxxxxxxxxxxxxxxx
From: Roberto Ragusa <mail@xxxxxxxxxxxxxxxx>
Date sent: Mon, 23 Nov 2020 09:12:32 +0100
Send reply to: Community support for Fedora users
<users@xxxxxxxxxxxxxxxxxxxxxxx>
> On 11/22/20 9:08 PM, Sreyan Chakravarty wrote:
>
> > dd if=/dev/vg/root_lv of=/mnt/exthdd bs=64k conv=noerror,sync status=progress
> >
> > 1) Why use noerror and sync?
> >
> > noerror might give me a corrupted image and sync is just going to increase the size of my image with padding.
>
> Indeed, noerror and sync are both bad advice, do not use them.
>
> >
> > 2) What is rationale behind block size?
> >
> > Will using 4M block size instead of 64K give me a different image? I need my image to be an EXACT COPY.
>
> Block size is for efficiency and 64k is better than 512, but since we are in 2020 go for 4M, it is the best option.
> The copy will be perfect even if the total size is not a perfect multiple of blocksize, dd is smart.
>
> Regards.
> --
> Roberto Ragusa mail at robertoragusa.it
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