[SOLVED] dd vs. e2image

newbiesforever · 02-08-2024, 09:35 AM

For copying a partition, I'm trying to follow someone's advice to use dd rather than e2image. The problem is that dd doesn't say how long it's going to take. I've seen dd run for hours for a 50 GB partition without finishing, whereas e2image clones it in maybe 15 minutes. Presently I'm giving dd another try. Should have remembered to start my stopwatch right away; but I know it's certainly taking longer than e2image. It's probably been half an hour.

lvm_ · 02-08-2024, 10:02 AM

Actually neither of them copies partitions - dd copies files and if a block device is selected it will copy it too, while e2image copies extN filesystems, and by copying only used blocks can do it faster and use less space. Could've been a good tool, where it not for its fondness of sparse files. Note that dd's performance can be greatly reduced by selecting a too small block size value, and copy progress can be checked at any time by sending USR1 signal to dd. And then there is fsarchiver...

newbiesforever · 02-08-2024, 10:11 AM

Quote:

Originally Posted by lvm_

copy progress can be checked at any time by sending USR1 signal to dd....

USR1 signal? And how do I send that?

michaelk · 02-08-2024, 10:18 AM

dd command has the status=progress option.

dd command technically copies bytes not necessarily files.

Petri Kaukasoina · 02-08-2024, 10:44 AM

Quote:

Originally Posted by newbiesforever

USR1 signal? And how do I send that?

Code:

killall -USR1 dd

lvm_ · 02-08-2024, 11:08 AM

Quote:

Originally Posted by michaelk

dd command technically copies bytes not necessarily files.

Code:

DD(1)                                                        User Commands                                                        DD(1)

NAME
       dd - convert and copy a file

SYNOPSIS
       dd [OPERAND]...
       dd OPTION

DESCRIPTION
       Copy a file, converting and formatting according to the operands.

pan64 · 02-08-2024, 12:27 PM

this is the first hit: https://askubuntu.com/questions/2155...progress-of-dd

michaelk · 02-08-2024, 12:54 PM

dd - disk/data duplicator

Since everything is a file the description is true but it can do a lot more.

https://www.linuxquestions.org/linux...ything_With_DD

You can copy a block device i.e. if=/dev/sdx or a partition i.e. if=/dev/sdxy but as posted it will copy unused space as well so if the partition is large it will take time.

fatmac · 02-08-2024, 01:04 PM

Basically, when using dd, give it a bs= (block size) - I often use 1G - the basic size is about 512 bytes if you don't, so will take a very long time...

lvm_ · 02-08-2024, 11:55 PM

Quote:

Originally Posted by michaelk

Since everything is a file the description is true but it can do a lot more.

No it can't. Block device is a file. Everything, absolutely everything dd operates on is files and it does exactly what is says in the man page, no less and no more. It is not dd which can do more but linux concept of a file is wider than in MS DOS.

michaelk · 02-09-2024, 09:31 AM

I can copy bytes from a tape drive.
dd if=/dev/st0 of=/whatever bs=512 count=1

I can copy bytes from a drive i.e legacy MBR
dd if=/dev/sdx of=/whatever bs=446 count=1

I can create an empty file by copying bytes
dd if=/dev/null of=/whatever bs=xx count=y

I can create an ISO image file from an optical disk
dd if=/dev/sr0 of=/whatever/

If a partition is a file i.e. /dev/sdxy then obviously it can be copied.

smallpond · 02-09-2024, 09:39 AM

Note the parameters you give to dd. if = input file, of = output file.

lvm_ · 02-10-2024, 07:23 AM

Quote:

Originally Posted by michaelk

I can copy bytes from a tape drive.
dd if=/dev/st0 of=/whatever bs=512 count=1

Yes, there are many wondrous things, and they are all files. It all comes into focus once you accept that everything starting with a slash is a file.

Code:

INTRO(4)                                                Linux Programmer's Manual                                               INTRO(4)

NAME
       intro - introduction to special files

DESCRIPTION
       Section 4 of the manual describes special files (devices).

FILES
       /dev/* — device files

pan64 · 02-10-2024, 07:31 AM

In short, everything which can produce and consume bytes (information) is a file. A directory will specify the location of it and the kernel will know how to read from and write to the given location or device.
Programs do nothing else, just read and write files and compute/manage the data (in between).

newbiesforever · 02-15-2024, 05:36 PM

Well, I'm now using that status=progress parameter. When dd reports a status such as

Code:

17179869184 bytes (17 GB, 16 GiB) copied, 537 s, 32.0 MB/s

, the status isn't entirely clear. Which GB is the amount of data copied, and which is the amount remaining? I'm guessing the first is the amount copied.