[SOLVED] Does mv do a lot of work (not a joke)?

stf92 · 11-27-2010, 07:21 PM

Kernel 2.6.21.5, Slackware 12.0

Hi:
Suppose I use the mv command to move certain subtree within the tree rooted at /. May I expect only a very small quantity of sectors will be involved in the process? Or, on the contrary, it is probable that a large amount of data will be transfered from sector to sector? Assume ext2.

If any of you is wondering why such a theoretical question, I am ready to translate it to practical terms: I have just created a directory called /home/john/mic2 which I expect to grow until reaching over a thousand nodes (nodes in the sense given to this word when studying lattices, trees and the like). But maybe later I will change its name to /home/john/mic1 for which, I think, mv is the usual tool in Linux.

mic2 is just a file. As such, there is a set of sectors associated with it. When I rename, these sectors will be left vacant and a new set of sectors will be written. Or maybe the same set shall be rewritten. And is that all? Remember mic2 is by now about a thousand nodes "large". Any hint will be welcome.

P.S.: If this does not belong to the forum, please tell me so or press the REPORT button and ask for the thread to be moved.

syg00 · 11-27-2010, 07:52 PM

Nothing will "move". A new name will be created pointing to the same inode.
Presuming same filesystem, and no oddities like symlinks.

stress_junkie · 11-27-2010, 08:00 PM

I just performed an experiment that confirms syg00's assertions.

Code:

$ mkdir test1
$ mkdir test2
$ mkdir test1/move-me
$ touch test1/move-me/1
$ touch test1/move-me/2
$ touch test1/move-me/3
$
$ ls -id test1/move-me
3244084 test1/move-me
$ ls -i test1/move-me
3244085 1  3244086 2  3244087 3
$ 
$ mv test1/move-me test2
$ 
$ ls -id test2/move-me
3244084 test2/move-me
$ ls -i test2/move-me
3244085 1  3244086 2  3244087 3

The inodes remain the same for the directory that was moved and for the three files.

stf92 · 11-27-2010, 08:09 PM

I think I understand. In the "directory" for /home/john, the entry for mic2 will have the name field changed to mic1. That will be the only change in the whole of /. Thanks. And BTW, the file in which mic2 consists (every thing in linux is a file) IS the inode, I now see.