A snapshot of your computer with dd, pv and gzip - Part 1 | Hacker News Reader

A snapshot of your computer with dd, pv and gzip - Part 1

allgood38.github.io

60 pointsadito32 comments

Consider using Clonezilla [1] instead. While dd will produce a sector-by-sector image of your medium (which can be terribly inefficient if you're using considerably less than 100% of its available space) Clonezilla is file system-aware for a number of common file systems and has built-in support for compression as well. It resembles the recently discontinued Norton Ghost this way but is fully FOSS.

I normally run it off a live CD/USB of Parted Magic [2], another tool I can wholeheartedly recommend.

[1] http://clonezilla.org/

[2] http://partedmagic.com/doku.php

I'd also recommend SysRescueCD that has these types of tools ready to be used as a bootable USB/CDrom image.

http://www.sysresccd.org/System-tools

I've used the imaging tools on the boot cd a few times to clone/restore hosts a few times without any issues. Very handy.

I created a SystemRescueCd screencast a while ago if anyone is interested [1]. Although, it does not look like SysRescueCD includes Clonezilla, there are tools like rsync, dd, and scp for moving files around in a pinch.

[1] http://sysadmincasts.com/episodes/3-systemrescuecd

I second the Clonezilla recommendation. Clonezilla is a monumental set of bash scripts that act as a "wizard" to drive a number of other programs. The most important one is probably partclone. You don't have to use Clonezilla to use partclone (it's packaged in linux distributions like Debian), but Clonezilla makes it easier.

http://partclone.org/

I would be concerned about how dd handles a bad sector that has not been reallocated by SMART. Many drives have 1 or 2 of these. Clonezilla is a good option because it also includes GNU ddrescue (so does PartedMagic) which can cope with most file system damage like bad sectors.

Just by the by, this is a terrible idea to do online. The best case is a crash-consistent replica. The more likely case is an inconsistent one that may or may not be repairable, because of the length of time it takes to do the dump.

If you want a bit-for-bit dump of an online filesystem, use Linux LVM to create a snapshot, then make an image of that (100% known crash-consistent) copy.

I don't always backup an entire system with 'dd', but when I do:

dd if=/dev/da0 | ssh user@rsync.net "dd of=backup.dd"

or maybe:

pg_dump -U postgres db | ssh user@rsync.net "dd of=db_dump"

"Stay thirsty, my friends."

Unless you have a really big upload pipe, better use ssh -C.

I don't know if ssh -C is strong enough these days. I use pigz or maybe pxz -1.

i'd look at using pv for the input, makes for a nicer output

pv /dev/da0 | ssh user@rsync.net "dd of=backup.dd"

I used dd booting from a USB stick to transfer a Windows install from hard drive to SSD this weekend - there are a number of steps that can be done beforehand to tighten up the size of the final output. These steps are also useful for virtual machines, but they tend to take quite a while...

(1) Defrag - built-in / maybe SysInternals contig http://technet.microsoft.com/en-us/sysinternals/bb897428

(2) Defrag the page file - SysInternals PageDefrag http://technet.microsoft.com/en-us/sysinternals/bb897426

(3) Zero unused space - SysInternals SDelete http://technet.microsoft.com/en-us/sysinternals/bb897443.asp...

(4) Shrink volume (if backup is filesystem-aware, and disk is one large volume) - http://technet.microsoft.com/en-us/magazine/gg309169.aspx

(5) After transfer, expand volume to fit target disk

Pretty much any utility automating these steps is acquired by the various virtualization vendors, or heads directly to the enterprise market (kind of like how inexpensive screencast creation software always disappears!).

Why would you possibly want to copy a pagefile over :D

Actually with the current RAM prices you don't need one at all.

Hmm, I'm a bit wary of this kind of backup, because it seems like it's nontrivial to recover part of your data if half of the backup goes bad. While the old fashioned rsync/copy all your files may be less efficient, you'll still have whatever it managed to copy if something goes wrong partway through.

This reminds be of doing a tar archive of all your files--if the archive is corrupted during that process, what then?

I use clonezilla to image the whole hard drive including OS once I have a 'clean' setup with an empty home and all my software installed.

Then I use rsync to copy all my 'stuff' back off a large external hard drive to the 'clean' installation. I try not to change OS to often :-)

Subsequently I use rsync with --delete set to sync the home drive only to an external drive of similar capacity to the computer drive for daily changes. This drive is ex4 and preserves ownership and permissions, and includes dotfiles.

Once a week there is rsync without --delete to a large external hard drive as 2nd backup. This drive is NTFS and does not preserve permissions and excludes dotfiles.

I have a free dropbox account for really crucial 'working' files. That gets rsync'd to a FAT32 stick each day using the 'time window' command so it does not write everything each time.

Basically the clonzilla whole drive backup is just to save time/bandwidth with re-installing and setting up. The rsync backup to the large drive is file readable on work PCs that use Windows should disaster strike. The 'sync' to the small hard drive is readable at file level on anything I can boot from a live CD.

Now, a bootable whole disc image would be of interest now and again.

Well actually, from a recovery point of view, you get some options. You can mount the image as a block device and perform operations on it. Say the image was corrupted, you could always try to mount the specific partition and run a fsck utility on it.

If you want to do something less tricky and low level than dd just remount the drive in question read-only and use tar. (be root to keep permissions, --use-compress-program=pigz)

On the restore side, you can just use pv like cat, and don't have to provide a size param:

  pv my.img.gz | pigz -d | dd (or hopefully tar xf - instead)...

In an ideal world a tool like pv could just look at /proc/fd/fdinfo/ instead of shuffling all the data through itself but I haven't found a tool that clever yet.

This is an incredibly naive way of backing up your system.

I use rsync to back up certain folders. I'm OK with re-installing Linux if my hard drive crashes.

It's not naive at all. There are a plethora of situations/reasons where one may want or need a block level image backup.

For example...

Well, it provides a perfect copy of the drive, not just a copy on another file system.

I've actually been able to restore to a drive, and when it boots its as though nothing ever happened. Plus its fast.

Its eerie to turn the computer on after knowing you formatted the drive for whatever reason, and your desktop pops up again.

It stops being eerie after a while. Several months ago, my brother was putting together a computer and wanted to test it (ie. the motherboard) before attaching any peripherals (other than the monitor). Obviously, installing the OS on the HD to do this was out of the question, so I just copied my computer onto a thumb-drive and used that. I didn't dd it, but just copied my filesystem over and did a grub-install.

The author mentions that removed files stick around on disk after being removed, and that this can increase the size of a compressed bit-for-bit copy.

They then suggest you can mitigate this by writing zeros to a file before rm'ing it. However, this is slow in the general case, and doesn't help if you've already rm'd the file.

As an alternative, the 'sfree' utility, available in the debian package 'secure-delete', can be used to fill the unallocated portions of a disk with zeroes (or random data).

sfree -llz <disk device>

will write zeroes to the free areas of a disk. -ll limits it to only one pass over the disk, and -z makes that pass write zeroes, instead of random data.

man page: http://manpages.ubuntu.com/manpages/lucid/man1/sfill.1.html

This is a pretty cool utility, I never really did like just creating a blank file, I'd rather use an explicit tool

I'll update the article.

On OSX, CarbonCopyCloner works really well :)

If you want to backup with this kind of technique, use partimage instead, and do so from a rescue CD. You need a quiescent filesystem for imaging, so it can't be under use by the running OS.

Partimag development has been dead for years; take a look at partclone instead. Another program with a similar goal but a different approach is FSArchiver.

http://www.partclone.org

http://www.fsarchiver.org/Main_Page

Remember that this cannot be run on a live system, since you'll get a corrupt image. Thus it's more useful for infrequent maintenance tasks than as part of a regular regime.

Hi! Author of this article here,

I've done something completely silly. I originally wrote this site on github, but then moved it over to a new host on its own domain and totally forgot about the old one.

If you like this article, please check it out here at:

http://allgood38.io/a-snapshot-of-your-computer-with-dd-pv-a...

At first glance it reminded me of this counter argument which warns about using `dd`, especially on a failing drive.

http://rachelbythebay.com/w/2011/12/11/cloning/

Pigz looks nice. First I've ever heard of it.

I just use BackInTime though, like TimeMachine I guess. It's really, really useful.

http://backintime.le-web.org/screenshots/

Looks like a graphical rsnapshot. Is this it?

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