kbr2000

The article sums up quite well which principles are at play here. The fun part it's suggesting (without words), is either to pick it apart and see what each part does, play around with the constants in there, or start from scratch and roll your own... (all with the Shadertoy linked below the article maybe?)

I would say most interesting texts (articles, books, school, ...) should leave stuff up to the reader's mind to figure out. That's how someone really learns. Versus pre-baked stuff like television etc.

If something does not resonate at first that's pretty normal. You could still take it apart and start investigating words or concepts that ring no bell, for example: waves, interference, demoscene, owls, Feynman.

Enjoy! ;)

Or rather:

> You must have a filesystem, located on the /dev/sda4 device, mounted at /mnt/lfs.

The /dev/sda4 device represents the fourth (primary) partition on the /dev/sda block device, which represents the first SCSI disk.

batshit?

It permits you to config more complicated backups more easily. You can inherit and override rules, which is handy if you need to do for example hundreds of similar style backups, with little exceptions. The same with include/exclude patterns, quickly gets complicated with just rsync.

It generates indices for its backups that allow you to search for files over all snapshots taken (which gives you an overview of which snapshots contain some file for you to retrieve/inspect). See dirvish-locate.

Does expiration of snapshots, given your retention strategy (encoded in rules, see dirvish.conf and dirvish-expire).

It consistently creates long rsync commandlines you would otherwise need to do by hand.

In the end you get one directory per snapshot, giving a complete view over what got backed up. Unchanged files are hard-linked thus limiting backup storage consumption. Changed files are stored. But each snapshot has the whole backed up structure in it so you could rsync it back at restore time (or pick selectively individual files if needed). Hence the "virtual".

Furthermore: backup reporting (summary files) which you could be piped into an E-mail or turned into a webpage, good and simple documentation, pre/post scripts (this turns out to be really useful to do DB dumps before taking a backup etc.)

You'll still need to take care of all other aspects of designing your backup storage (SAS controllers/backplanes/cabling, disks, RAID, LVM2, XFS, ...) and networking (10 GbE, switching, routing if needed, ...) if you need that (works too for only local though). Used this successfully in animation film development as an example, where it backed up hundreds of machines and centralized storage for a renderfarm, about 2 PBytes worth (with Coraid and SuperMicro hardware). Rsync traversing the filesystem to find out changes could be challenging at times with enormous FS (even based on only the metadata), but for that we created other backup jobs that where fed with specific file-lists generated by the renderfarm processes, thus skipping the search for changes...