On 4/01/2013 8:30 PM, tonyalbers wrote:
> Ok, it seems to me that there is some confusion of which kind of dedupe I'm 
> referring to.
>
> What I'm talking about is variable-length block-based target dedupe, that is, 
> the DXi or DataDomain box receives all data from the client via the backup 
> server (bacula SD) and then handles the deduplication and compression of 
> these data. There is no dedupe or compression on the client or backup server 
> itself of any sort.
Just to be sure, the targets are file volumes on LUNs or the like?  The 
storage is not behaving like some sort pseudo-tape device?

And compression is not enabled anywhere in any Bacula configuration file 
and the entire Bacula process chain has been restarted?

Spooling is turned off as well?

> This does not work in practice right now, since bacula does something to the 
> backup stream that makes most of the blocks or segments unique.
Bacula was initially designed to be as efficient as possible when 
writing to *tape*, it chunks up data before it is written, anything 
could cause a shift that reduces similarity.

> I've tried this on a DXi and on a fileserver using SDFS, and both had only 5% 
> data reduction after running three 6GB backups of the same filesystem on a 
> client. In theory that should give us at least 66% data reduction ratio.
I am surprised that it is so low, I would have expected more.

Oh, what happens when you just "tar" the filesystem to the storage 
several times?

> Please bear in mind that target dedupe is pretty much the industry standard, 
> since RTO plays a huge role in deciding what type of backup and storage to 
> use.
There are *no* standards, just whatever the vendor is peddling.

        Cheers,
                Gary    B-)


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