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Re: Suggestion for Syncany


Hello David,

we have opened a Blueprint for this idea. We'll concentrate on it as
soon as we released a stable version -- and I'm sure we'll get back to
you and ask you for advice :-)


On Sun, Jun 5, 2011 at 1:14 AM, David TAILLANDIER
<david.taillandier@xxxxxxxxxxxxxxx> wrote:
>> I apologize for my late e-mail
> Not a problem. I just emailed you in case this idea could be of any use.
>> If I have 3 different storages, and I'd like to store 10GB, I would
>> create parity files for these 10GB with ~34% redundancy (--> 10GB + 3,4
>> GB parity files). I would then split the 10GB in 3,33GB parts and upload
>> them to the three storages (together with one third of the parity
>> files), i.e. each repository would get 3,33+3,4/3 = 4,46 GB of data. If
>> now one of the storages fails, I can still restore 100% of the data. Did
>> I get that right?
> In overall you're right. But you miss something very important: the real
> potential is the fact you can set the loss percentage as you want.
> With 3 storage locations you can set it to 0% or 33% or to 66% (other values
> are not sensible for 3).
> 0% = usual way to store things
> 33% = sort of RAID5
> 66% = you can loss 2 storages locations without having problems (at the cost
> of more transfert, time, money, etc)
> Let's say you have 10 storage locations, you can set the acceptable loss
> from 0% to 90% by 10% steps.
> Can you imagine to loss more than 2 storage at the same time ? If not, then
> you have 20% acceptable loss. Set it to 30% to be sure. This is nearly
> indestrutable.
> The hard thing is:
> - not every storage locations are of equal size
> - the user don't want the same amount of security for every data
> - with many storage locations, this is not mandatory to save everything
>  into every location
> Each of those can be optional. But if you can deal with this, you're the
> king :-)
> Storage locations of equal size:
> solution 1: use the smallest size for all
> solution 2: compute the resulting loss factor for each size (ideal)
> The user don't want equal security for all:
> solution 1: don't let him set different levels for different datas (but
>            what if he change his mind ?)
> solution 2: ... I don't know your software enought for that  :-)
> This is not mandatory to store everything everywhere (usefull with tons of
> storage locations).
> This is totaly dependant of your algorithm, so nothing can be said now.
> Feel free to ask me anything. But as I'm not a good programmer, I think I
> gave my max already.