Les Mikesell wrote:
> On Mon, 2006-11-06 at 14:54 -0800, Mark Schoonover wrote:
>
>>> Note that this only works as a backup if the original filename is
>>> removed. If it is overwritten or truncated instead, all links now
>>> point to the changed version.
>>
>> This is true if you're doing it with only filesystem tools, but this
>> system is using rsync. What's happening is the cp -al occurs first
>> making hardlinks that point to an hourly directory into the current
>> directory, then rsync is run to update current. Because rsync will
>> create a new temp file when any file changes, the original is
>> deleted with it's data 'pushed' to any hardlinks pointing at the
>> original file. Rsync then renames the temp file the original file
>> name that has changed, therefore assuring that any hardlinks will
>> always have the previous copy of any changed files. With rsync
>> running in --delete mode, any files from the source server that get
>> deleted, will get deleted out of current in the backup server,
>> causing this cascade of hardlinks to get updated with the deleted
>> files data. That's how this system can create incremental backups of
>> only changed data, but with hardlinks, it looks like full backups
>> are made each and every time. Really saves disk space, that's for
>> sure!
>>
>> Hope this clears things up...
>
> Backuppc is even more extreme in the space savings. It first
> compresses the files, then detects duplicates using an efficient
> hashing scheme and links all duplicates to one pooled copy whether
> they came from
> the same source or not. It includes a custom rsync on the server
> side that understands the compressed storage format but works with
> stock versions on the remote side so you don't need any special client
> software. And it has a nice web interface for browsing the backup
> archive and doing restores.
Sounds like a good product! Since I had plenty of terabytes of storage,
having compression on the files wasn't a requirement. One of my requirements
was not having a gui to configure things, or do restores. Thanks for
pointing some info out on backuppc, I've never heard of it.
Mark
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