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I know that it's very important to keep backups of everything as regularly as possible, but I was just wondering how many different versions of the backup/from how long ago I should keep, because obviously they do take up space but there is also the possibility that an infection/problem may have been backed up in the most recent back up.

I realise that this may be down to personal choice but is there any recommendations or justification behind how many backups of the same thing you keep?

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closed as not constructive by haimg, TFM, ChrisF, sudo, Tanner Jan 21 '13 at 2:25

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This is unfortunately very subjective, varying both on the data you have size-wise, its importance, and so forth. You may even want different regimes for different chunks of your data: syncing your collection of large photo files with your offsite backups weekly (or on-demand as you add a new set from an outing), but synching documents and financial stuff daily.

As for how many versions you have to remeber that a backup deals with two very different sets of fault scenarious: hardware error and human error. For the hardware dying situation you only need the one good backup, so at least two (in case the failure happens while updating the current one), preferably the traditional three. For covering human error it isn't a case of how many copies to keep, but how far back those copies should go. If you were to accidentally delete a file for instance how long would it be before you noticed? You need a backup going that far back plus a little. A not uncommon choice is three daily copies and three monthly ones, but there are no hard and fast rules (or even genberally good rules of thumb) here - only you know how important your data is and so how much effort you need to take to protect it.

Personally I use snapshots-via-rsync using a technique similar to those covered in http://www.mikerubel.org/computers/rsync_snapshots/ (the article is old, but still relevant) - there are other ways to acheive a similar effect too which might be easier if you are a beginner (http://rdiff-backup.nongnu.org/ seems popular, but I've not used it myself so can't comment more specifically). I have monthly snapshots going back over a year and daily ones for over a month, and as most of it doesn't change much it doesn't take all that much space than a complete copy or two. An important thing to consider with any solution like this though is that corruption in your backup set can affect all snapshots at once, so I recommend at least two disconnected copies of the data so you have at least two physical copies of each file meaning corruption in one of your collections of snapshots doesn't affect all the "copies" you have.

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Hi, apologies for my very slow reply and thank you for your answer - it made an interesting read. I did fear that this question would be rather subjective - however I did think that it would be one that other people may benefit from nevertheless. It's unfortunate that this question has been closed now but seeing as though it has, are you able to provide any good links relating to different backup schemes? And just to clarify, are any of the backups you keep incremental? Thanks again –  Andy Jan 24 '13 at 17:18
    
A series of snapshots produced using rsync --link-dest or rsync+cp -al is effectively an incremental scheme in a number of ways. Backups are a complex area - anyone who says they have a one-size-fits-all (or just one-size-its-most) solution is wrong. You are better off starting with "if disaster X happened, what would I lose, and is that acceptable" and then consider technical solutions to changing that. You might find wikipedia a good place to start (en.wikipedia.org/wiki/Backup) –  David Spillett Jan 25 '13 at 10:06
    
One other note: if your backups are partly to cover security issues, and that generally is a concern these days given how connected everything tends to be, make sure you have regular offline copies or other such protection. If all your backups are online, otherwise you might be in the position where malicious code (or a malicious person) can damage both your live data and all your backups at the same time. –  David Spillett Jan 25 '13 at 10:07
    
Thank you very much for your answer and comments. They have been very useful and have helped me to make a decision! –  Andy Feb 2 '13 at 16:51

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