Richard Freeman on 7 Dec 2009 10:43:32 -0800

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Re: [PLUG] Self-hosted online backups?

brent timothy saner wrote:
> 3? YEP! and it DOES NOT negate #2. taken from their wiki[2]

I'm not sure that anybody has suggested that you can't both compress and 
encrypt data at the same time.  In fact many encryption utilities like 
gpg do a compression round first to make the encryption harder to break.

However, the benefits of that compression cannot cross the boundaries of 
any individual client.

> 5? yep. of course, "efficient" is a bit of a relative term, but for what
> it does 

That is where I'd argue that any client-encrypted system that does not 
trust the server cannot be as space efficient as a system which does 
trust the server.

It is all relative as you suggest.

For example, suppose you back up 100 windows boxes that have a 2GB 
OS/application install and a 5 MB of unique data each.  With the 
untrusted but compressed model you're going to need about 100GB of disk 
space to back that all up (100*2GB/2).  For the trusted model you might 
get away with as little as 1.5GB ((2GB+100*5MB)/2).  In practice stuff 
like service packs and variation will cost you a few GB, but you're 
talking about a fraction of the space of the client-encrypted model.

If you fall somewhere between the extremes of having a single computer 
at home, or a datacenter with 500 cloned server images in it, choose 
what makes the most sense for you...  :)
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