On 11/22/20 9:31 PM, Jon LaBadie wrote:
On Mon, Nov 23, 2020 at 01:38:34AM +0530, Sreyan Chakravarty wrote:
Hi,
I use LVM on top of LUKS.
My entire root file system is on a logical volume. I have no seperate home
or swap partitions.
I would like to know how can I clone this logical volume to my external
hard disk.
I have seen commands like :
dd if=/dev/vg/root_lv of=/mnt/exthdd bs=64k conv=noerror,sync
status=progress
I have a couple of questions about this:
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.
Why 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.
Does dd write a complete final block to the destination. If so, the image
would not be an exact copy unless the source size is an exact multiple of
the blocksize.
Unless "conv=sync" is used, it does not. Without "conv=sync", when the input
reaches EOF, dd will write whatever partial block has been read. If you _do_
use "conv=sync", then that output block will be zero-padded to the obs size.
If the output is to a device and not a file, that might cause a superfluous
"out of space" message and a failure exit code. If output is to a file, then
the resulting file could be larger than the source.
The status message from dd indicates the number of complete+partial blocks
read and written, e.g.:
1201+1 records in
1202+0 records out
showing an output block that was padded to the full block size.
--
Bob Nichols "NOSPAM" is really part of my email address.
Do NOT delete it.
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