Thank God for backups!

[Daniel Carrera]

Vincent Trouilliez wrote:
>>Ubuntu has an easy to use backup tool, I highly recommend it. Install it 
>>right now, don't wait! : sudo aptitude install sbackup
> 
> THANK YOU !
> 
> I always felt that a simple to use GUI backup system should be one of
> the core components of a Desktop OS. I just installed sbackup and it's
> indeed excellent, it's a dream come true: all the features I had in
> mind, in a clear and easy to use GUI. Simply lovely !

:-D

> Now I just need to fork out soe cash to buy a big hard drive to host the
> back-ups. I have about 25GB of data in /home, but I wonder how much
> space the backup system needs exactly for operating properly. 30GB, 50,
> 100, no idea.

Oh, that number can vary wildly depending on your backup strategy. I'll 
try to help here. Let's use 100GB as a base estimate.

Choosing a backup strategy is a trade off between the following:
1. Disk space.
2. How much work you put in when you need to recover a file.
3. How often you want to backup your files.

The good news is that 'sbackup' makes (2) easy, so we can afford to 
optimize disk space more. sbackup offers two types of backup:

* Full backups - copy all 25GB (they'll be compressed, estimate 15GB).
* Incremental backups - only copy files that have changed since the last 
backup.

So, if you do incremental backups every day, it will only copy files 
that changed *on that day*. So, instead of backing up 25GB it might 
backup only 20MB. Hence, doing more incremental backups and fewer full 
backups significantly reduces the amount of disk space needed. But when 
you need to recover a file, you need to look at every incremental 
backup, from the most recent backwards, until you find the one that has 
the file you need.

Practical example:
------------------
* I need to backup ~1.5GB of data.
* Incremental backups every day.
* Full backups every 14 days.
* Each full backup takes ~789MB.
* Each incremental backup takes ~32MB.
* My since March 16 take up 3.7GB.

In your case, you'll want to do full backups less often. Let's try to 
make a ballpark estimate:

* Say you make full backups every 30 days.
* Say that each full backup is 15GB after compression.
* Say that each incremental backup is 50MB.

Then 100GB will give you 6 months worth of backups.

If, instead, you make full backups every 60 days, then 100GB will give 
you about 11 months of backups. On the other hand, if you did full 
backups every 14 days, then 100GB would last you only 3 months.

Cheers,
Daniel.
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