[tahoe-dev] Tahoe performance

Francois Deppierraz francois at ctrlaltdel.ch
Sat Feb 7 16:13:18 UTC 2009


Hi Andrej,

A few comments inline.

Andrej Falout wrote:

> Link: 2.5MB/s down, 0.2MB/s up (According to speedtest.net, this is
> faster then 98% of all Internet connections they measured)

Well, uploading 50 GB at full speed will take at best 3 days with an
uplink of 1.6 Mbps (0.2 MBps).

> [1] Duplicity, or any other tar based backup is unfortunately not an
> option (for me) because:
>  - full backup file download requirement to restore even 1 file, which makes it
>              a) requires free space on target PC (at least) equal to
> the size of whole backup file to both backup and restore
>              b) Bandwidth is not free, and in anything less then ADSL2
> downloading 50GB is irrational, making it useless for
>                      restoring important business document while
> traveling and on wireless Internet. Heck, downloading 50GB to
>                      restore one file will always be irrational. Plus
> waiting for 3 days to be able to get a file is just not acceptable.

I don't agree on this point. By default, duplicity stores data in 5 MB
chunks (.volX.difftar.gz) and uses indexes (.manifest) to retrieve only
chunks required to restore the files you specified.

>  - backup running 5 days will most likely get interrupted at some
> point and cannot be resumed

5 days is not that far from the theoretical maximum in your case of 3
days I just mentionned.

During my tests on the allmydata.com grid I experienced a maximum
throughput of 1 Mbps from Switzerland even thought my uplink is 5 times
faster than that.

>  - Makes the whole Web Browser interface to virtual drive virtually
> useless, and the whole "virtual drive" concept pointless.

Yes ! This is why the great backup which just implemented by Brian
Warner is so awesome, thanks Brian !

François



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