> Craig wrote: > I don't understand what having links for files in the backup > gets you over having a copy of the files in the backup.
I get 31 days, each of which is a _full_ backup, in typically about 2 times the drive space of ONE copy. > Would that not make a backup worthless precisely because you > would not have copies of the files on the backup? Well, no. Warning - the following is deep techy. Proceed at your own risk. *smiles* On a EXT (2,3, or4) file system (and some others - not sure which), a file in not referenced by it's name but by an identifying number called an "inode" Next, a file name is actually the full-path. That is the name of the photo is not really "shiny-T123.jpg" but "/home/fmiser/photos/cars/mercedes/wagons/shiny-T123.jpg" Then, that full filename is just a link to an inode. And an inode can have any number of links, each with a different (full) filename - but for practical purposes, the link takes up no space. Finally, "deleting" a file is more correctly called "unlinking" - that is, removing a link. And until _all_ the links are cut, the inode is still "active" and the file spaces is not declared available for re-use. So at the time of backup, I use rsync to make a copy of all the various files to a drive (or RAID array) in a directory called "00". Then I use "cp -al" to make a copy of "00" into, say "26" (today). Tomorrow, when "00" gets updated to match what is live, files that have changed will have there links to inodes changed - or cut. But files that have not changed will retain the existing inode link. If a file hasn't changed over the whole 31 days (like the shiny T123 photo) then it only takes up the space of ONE copy. But, the real beauty is that each one of the 31 days is not an incremental backup. Each one is a full and complete copy of the live file system on that day. So if I point a file manager at any one of those 31 days, what I see is all my files and all my directories. Yet because the inode is the same for all the days that the file did not change, the whole 32 directories (00 through 31) typically take up about not more than 2 times the space of just one day. _______________________________________ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
