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. Gdisk reports my root filesystem is 240197632 1K blocks long.
$ factor 240197632
240197632: 2 2 2 2 2 2 2 2 2 2 2 2 2 109 269
So 2^13, or 8KB is the largest block size where input and output would match.
Again, this assumes dd writes a full final block. Possibly a bad assumption
Jon
--
Jon H. LaBadie jonfu(a)jgcomp.com