On 11 September 2010 17:13, Les Mikesell <lesmikesell AT gmail DOT com> wrote:
> On 9/11/10 2:22 AM, Timothy Omer wrote:
>>
>> -for rsyncd, fulls and incrementals are the same other than the fact
>> that full takes longer checking all files. The reason full is the same
>> is due to it will not transfer any files in the pool that are the
>> same, hence it only transfers changes... just like incrementals
>> -if have 1 full and 7 incrementals, the next full will hard-link back
>> to any full and incremental backups it needs to use. Therefore not all
>> files will be transferred again
>
> It's not 'any files in the pool', the server-side comparison is done against
> your last full unless you have configured incremental levels. Any files
> that weren't in the last full get transferred, then discarded when found to
> match an existing pool file (the hashing for the filename match can't be
> done otherwise).
>
>> -when an old backup comes up to expire, I guess any files that are not
>> hard linked are deleted - not all of them
>
> Yes, the nightly run removes pool files with only one link remaining (the
> pool filename).
>
>> You said "why not just do more frequent full runs to keep the base
>> more current?" - why is this different than incremental? Full and
>> incremental to me just sound more logical and the extra time on the
>> client to do the processing of a full I can schedule for a weekend.
>
> Fulls rebuild and fill the complete file tree for a backup and become the
> next comparison base where incrementals just hold the differences. If you
> can run fulls on weekends - or skew the days they run so they complete in a
> reasonable window you shouldn't need the extra hardlinks to fill
> incrementals.
>
> If you use the tar or smb xfer methods, you also need frequent fulls to be
> sure you catch all the files, since those incrementals are strictly
> timestamp based and will miss new/moved files if an old timestamp is
> maintained. Rsync/rsyncd doesn't have that issue since it actually compares
> directories.
>
> --
> Les Mikesell
> lesmikesell AT gmail DOT com
>
>
Hey Les, ok think I got it.
So when an Incremental runs, if the last backup is a Full backup files
that are the same never get transferred to the server. If the last
backup was Incremental then any files that have not changed since the
last Incremental will be transferred to the server, but then dropped.
Therefore you still get the space saving as the files will be hard
linked, but you will not save in bandwidth.
As you said, just doing full backups will mean I only transfer data
that changes. One of the benefits of having multiple traditional full
backups is that that you can have the same file backed up twice, that
covers you if one gets corrupted - but as BackupPC hard links all
duplicate files that will never be the case (sorry if that sounds
silly, but just confirming)
Sorry if this sounds like im repeating what you have said, but
confirming this in my own words is amazingly helpful!
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