On 6/7/2011 11:22 AM, Boniforti Flavio wrote:
>
>> That's a problem that a sufficient amount of money can solve, with
>> 'sufficient' varying wildly depending on your location and network
>> providers.   But in any case it is likely to be more efficient to back
>> up the live machines (virtual or otherwise) than their disk images - and
>> that way you also get useful pooling for the storage.
>
> Well, I don't know *why* they ask me to do integral backups of their images,
> but I simply can guess: it's because they eventually want to be able to go
> over to that remote location with their USB HDD and copy that image over,
> place it on the server and run it!

That makes sense in terms of being conceptually easy, but it still may 
not be practical to get clean copies in a given time span.

>> One other point that I'm not sure anyone mentioned yet is that the rsync
>> comparison is normally against the previous full run, so it will be
>> important to either do only fulls or set incremental levels to make each
>> run backed by the previous so the differences don't accumulate over time.
>
> Could you please depict a bit more in depth this part?
> AFAIU, if I do too many incrementals I'd have to take in account growing
> backup times from differential to differential.
> On the other hand, if I'd do only full backups, I'd have way longer backup
> times, for *each* single backup shot.

There is a tradeoff between the way files that have and haven't changed 
are handled.  In an incremental, unchanged files as determined by 
timestamp/length are skipped quickly where fulls will read through the 
file contents doing a block checksum verify.   Changed files are 
processed by sending the differences from the previous full or 
appropriate merged incremental level. Full runs rebuild the tree for the 
next comparison.   If you are backing up a directory of images that all 
change on every run, you might as well do fulls every time.  If only a 
subset of the files well have changes then incrementals will be faster 
but you have to rebase the tree eventually.  If they do something like 
copy each image snapshot to a new filename (perhaps with a timestamp), 
there won't be any good way to handle it.

-- 
   Les Mikesell
    lesmikesell AT gmail DOT com

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