Hi Gabriel & list, On 10/29/13 00:45, Gabriel Kerneis wrote: > I have a question about daily bandwith usage. On my admin interface, I see: > > Server->Client ≃ 3.7 × Client->Server > > I wonder if this expected, considering that I am only creating (and deleting > in > a round-robin manner), never restoring archives. I am slightly surprised that > the amount of control data would be so large, but this is just a naive > question, > I didn't study tarsnap source code.
I think it's the other way around: The amount of data being uploaded is so small. When you create an archive, tarsnap deduplicates everything locally and only uploads new blocks. Most of those blocks are (~64kB of) data; some are metadata consisting of lists of (~1600) data blocks. If you have enough (~100 MB) of unchanging data all together, the metadata block listing the data blocks will be identical to a previously stored one, so that won't be uploaded again either. When you delete an archive, tarsnap needs to download all the metadata -- all the lists of blocks -- so that it can adjust its reference counts locally and figure out which blocks need to be deleted. As a result, the download bandwidth used by deletes depends only on the size of the archive -- not how well it was deduplicated when it was created. If you use the --print-stats option when creating archives, I think you'll find that the total size of the archive you're creating is much much larger than the amount of new data being uploaded. > Could this indicate an issue with my local cache? No, I can't see any possible connection there. -- Colin Percival Security Officer Emeritus, FreeBSD | The power to serve Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid
