My favourite mnemonic for dd is still “disk destroyer”, though.
Someone told me this years ago and I assumed it was the actual origin of the name for the longest time.
For the lazy (from wikipedia):
The name dd is an allusion to the DD statement found in IBM's Job Control Language (JCL), in which the initials stand for "Data Definition".
Yes, I believe this is the actual origin. The ‘if=’, ‘of=’, and so on is a reference to the syntax accepted in JCL.
dd if=/dev/random of=/dev/root MUAHAHA :)
(Always fun when you have a Linux CD and need to nuke a disk.)
[Comment removed by author]
Why do tapes need to be written to using a specific block size? Aren’t the ribbon-like?
Why do you use tapes over, say, USB flash drives? Or hard disk drives?
15 TB for $200, the media’s designed to be moved around independent of the mechanism, and if you already have the organizational structures to deal with them you can just keep on keepin' on.
On top of hga’s comment, some groups tracking reliability of media point out that most media has far lower reliability than they advertise. I’ve seen CD’s or DVD’s stop working after a few years of just being in storage. The archivists that have been in the game a long time prefer tape if we’re talking cost & reliability. One also pointed out that damaged media is easier to deal with: snip, snip. Now you just have less tape & lost less GB per square inch. The losses & recovery of HD data is a tad worse.
One other thing about long-term storage is that it really should be long term. The vendors have to be around supporting it in long term. There’s been tons of critical stuff put into tape by big companies and governments. That implied they’d continue to improve with backward compatibility or at least ability to move data between mediums. That’s what they did. The latest, greatest technology might disappear with their vendor a few years from now. If it’s to be future-proof, should go with as conservative choices as one can.
EDIT to add link showing they strongly push backward and forward compatibility. Plus, it’s $114 for 6TB. I like those numbers.
My only wish is that this article kept digging a bit. The author was developing a really interesting line of inquiry here and I’d have loved to have seen it taken further.
One of the overlooked features of dd is the output flag option. Imagine you are on a server running a bunch of VMs and you need to copy a PV. Using dd if=source.img of=/dev/something bs=1M will work nicely until you notice that you are slowly running out of memory. Not a good idea to provoke OOM killer into action. Luckily you remember to add the magical oconv=direct flag to indicate that you do not wish to buffer on the output side and voila, everything is working fine again. Same thing goes for copying images to slow USB drives.
dd if=source.img of=/dev/something bs=1M