First things first, I'm new to server administration.

How are backups stored nowadays? In another internal HD used just for this purpose? On an external HD? Assuming that I do not have a backup server.

Also, I have learned that differential backups are slower to back up the data but faster to restore, because it's only needed two disks, the full backup and the last differential backup. By contrast, an incremental backup is faster backing up files but slower on restoring because I need to use all previous disks.

However, this approach seems to be very old, when backups were stored on tapes. Is there still a huge difference between restoring a differential or an incremental backup?

Finally, which software is recommended? Or do you use rsync only? On my own computer I use rsync on mirror mode (-av --delete) for daily backups, but don't know whether it's appropriate or not to use it in the enterprise scope.

Assuming that you don't have a backup server I'd buy a tape drive and plug it in directly, you can take the tapes home with you as an el cheapo "off site storage". External disks are just as likely to fail as internal disks, especially if you drop one - you don't have to be that gentle with tapes.

You could choose to buy a NAS with raided disks, but this prevents storing your backups offsite. You could work around this by pushing your backups to some cloud storage, but you'll have to think about encrypting them first (probably required) and whether the transfer speeds are sufficient to meet your recovery SLA in the event that you need to get one back urgently.

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Probably overkill, but what we do is this, it may give you some ideas.

We use dirvish to backup up data from 37 servers in 4 locations to a central "backup server".
We keep a rolling 6 months of data on the server.
Using dirvish allows us to have the most recent "vault" having pretty much an image of the relevant data with the older "vault" having just the older versions of files etc.
From this backup server 3 daily LTO4 tapes are taken and rotated off-site with a commercial storage company. The data is encrypted as it's written to tape. We use an HP autochanger and barcoded tapes so there's no need for an operator to check and change tapes around except first thing in the morning.
At weekends we take an additional tape with less critical data.
Monthly we take the 4 tape backup and leave that off-site for our data retention period.

All of this is done with a bash script for portability.

Future plans involve either upgrading to LTO6 tape drives (to make use of TFS and on-tape encryption) or using a commercial "cloud" storage provider for additional resiliance.

Like I say.... bit of overkill but it might give you some ideas.

(I'm old fashioned, I LIKE the idea of physical tapes stored off-site that I can have delivered to a DR site and restored to a server, rather than having to pull things over the internet from a cloud over the wire.)

What do people think about Tandberg RDX?

My thoughts are:

Pros:

Sensitivity is much less i.e. the media and the drive are less prone to maintenance issues i.e. dust and dirt. I used to work for an IT company whereby some of their customers had problems with dust in drives which can spread to the tapes and vice versa. Having a removable disk that is more like a cartridge in my opinion is more robust than tape.

Direct access not serial access like tape (efficiency and speed of data transfer)

Cons: Capacity and cost.


There might be other issues; if anyone has any thoughts I would invite them to express these.

Looks interesting and Tandberg have been around for years so they've a history in this kind of thing.

At the end of the day the media is still a hard disk, just doesn't look like one, so the normal things about moving parts etc. apply.

As for direct access. Relevant if you're looking to restore a single file rather than a complete back-up I suppose.

It also looks rather "propriatory", with something like a widely adopted standard like LTO there's the freedom to use different vendor devices which some might consider a plus.

The 8 drive unit looks interesting though!

At around $250 for the 1.6Tb media that's 10x the cost of comparable tape media.

It depends on what risks you are trying to guard against. Backing up to another internal HD protects you from file losses within the primary hard drive, but it doesn't protect you from a malicious user who has access to both drives, nor does it protect you from physical theft of the computer (or physical loss due to fire or other catastrophes). That's why you should consider using a backup server and/or off-site backup.
Mirror mode covers you if a file loss (or corruption) is discovered before the next backup. Otherwise the loss is mirrored in your backup. With incremental backups, you can restore even if the loss is not discovered until days later.

It is possible to use rsync for incremental backups. Briefly, each daily backup goes into a sequentially-named directory, and is hard-linked to the previous backup by using rsync --link-dest. With this method, differential and incremental are equally fast to restore, but incremental uses less disk space and therefore is slightly faster to back up.

This is the underlying method the dirvish tools use, as having additional facilities for "aging" of backups etc. without having to write your own scripting for it.