Daniel Carrera wrote:
> Holger Parplies wrote:
>> 1.) That is what you are requesting BackupPC to do.
>>     If you want your backups to depend on a different reference point
>>     than the previous full backup, you can use IncrLevels. An incremental
>>     backup *can* miss changes. That is highly unlikely with rsync but
>>     remains possible. With increasing level, chances increase. So, doing
>>     *exactly* as requested makes sense.
>>     As with any backup scheme, only full backups are completely reliable.
> 
> How can it miss changes? How do full backups fix it?

The smb and tar methods use file timestamps to determine which files to 
transfer.  They'll miss new files with back-dated times (like you get 
with unzip, etc.) and the new locations of old files under a renamed 
directory.  And those methods don't have a concept of files that were 
deleted since the last run.  Full backups fix it by copying everything 
(and it doesn't wear your network out...).

>> 2.) Backup dependencies
>>     A level 1 backup cannot depend on any other level 1 backup (because this
>>     other backup can - and probably will - expire first).
> 
> This is something else I don't understand. Why does it create 
> dependencies? I thought BackupPC did something functionally equivalent 
> to my hand-links method.

It does that for fulls.  For incrementals the tree just holds the 
changes, saving a lot of work.  On a small scale server that might not 
matter. For one close to capacity, it does.

> With my method, I can safely delete any daily 
> backup with full confidence that the others won't be affected, as I'm 
> just deleting hard links. As long as a block of data has at least one 
> hard link pointing to it (ie. as long as I need it) the file will be 
> safe. I thought that BackupPC did something that was functionally 
> equivalent with its pooling thing.

Again, that's true for fulls - and it knows what it needs to keep to 
support the incrementals.  There is one more layer of complexity here 
though.  There is an  additional hard link in the cpool directory that 
is used to match up new copies of the same content - so these links need 
to be removed when the link count goes down to 1, meaning no backups 
reference it.

-- 
   Les Mikesell
    lesmikesell AT gmail DOT com


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