![\"Full,](\"https:\/\/nsrd.info\/blog\/wp-content\/uploads\/2012\/02\/diff_2incr_level5.png\" "\\"Full,")
<\/a>This represents a full backup (which is drawn as a “line in the sand”), two subsequent incrementals, and a level 5 backup following the second incremental.<\/p>\n
The first incremental backs up everything that has changed since the previous backup, which in this case is a full, thus the end-point for its arrow is the full backup line. The second incremental again backs up everything that has changed since the previous backup – the first incremental. As such, its arrow end-point is the first incremental backup.<\/p>\n
Finally, the level 5 backup bypasses the incrementals and backs up everything that has changed since the full, so its arrow end-point goes all the way back to the full.<\/p>\n
If you’re wondering about what makes the differential level 5 significant there – nothing. It doesn’t matter whether you use a 5, 3, 2, 8, etc. The differential numbers only have significance when you use more than one of them in a single schedule. For instance, the above backup could have been equally achieved with:<\/p>\n This allows us to establish our first set of criteria for differential levels:<\/p>\n Rule 1<\/strong>: If only using one differential level in a schedule, the number is irrelevant.<\/p>\n Guideline 1<\/strong>: If only using one differential level, start in the middle. That way, if you have to slot in another differential level later, you’ve got room on ‘either side’.<\/p><\/blockquote>\n Differentials in NetWorker become more complex when you have more than one level involved. Let’s consider a slight change to the above level diagram:<\/p>\n In this, we’ve got a fairly standard appearing set of levels until we hit the differential level 1; this follows a 5, and backs up everything that has changed since the full. If we turn to the nsr_schedule<\/em><\/strong> man page for a clarification here, we see:<\/p>\n “The levels 1 through 9 cause all files to be saved which have been modified since any lower level was performed. As an example, if you did a full save on Monday, followed by a level 3 save on Tuesday, a subsequent level 3 save on Wednesday would contain all files modified or added since the Monday full save.”<\/p><\/blockquote>\n So this leads to our second set of criteria when dealing with differential levels:<\/p>\n Rule 2<\/strong>: Any differential level will backup all files which have been modified since any lower has been performed.<\/p>\n Guideline 2<\/strong>: Think of a full backup as ‘level 0’, and the differential rules make more sense.<\/p><\/blockquote>\n Thus, if we swap around the two differential levels in the above diagram, our backup behaviour becomes markedly different:<\/p>\n The behaviour up to and including the level 1 backup mirrors what we saw in figures 1 and 2 \u2013 incrementals going back to the full, and the first differential performed also going back to the full. However, the level 5 backup will only backup those changes which have occurred since the level 1 backup – 1 is lower than 5, so it will “cause all files to be saved which have been modified since any lower level save was performed” to be triggered when the 5 is run.<\/p>\n<\/a><\/a><\/a>