Re: [rdiff-backup-users] rdiff-backup painfully slow using NFS mount

[Simon Hobson]

Josh Nisly wrote:

> You are correct in your analysis. Using rdiff-backup locally + rsync 
> to the NFS mount would certainly work.

Wouldn't that still leave the same fundamental problem - that using 
NFS rather than rsync or rdiff-backup to access the backup storage 
means that the system has to read the files from storage across the 
network in order to work out what needs to be copied ?

Ie, taking the earlier example I gave (in thread "Measuring transfer 
size") of adding 1 byte to the front of a 1G file :

If using an rsync server or rsync via ssh remote, rsync would 
determine that the file contents had moved by 1 byte and would 
transfer across the network only an initial block of data plus all 
the checksums required. Ie only a few k traffic

If mounting a filesystem via <insert file sharing method> would mean 
rsync reading the entire 1G file across the network, calculating that 
it needs to insert 1 byte, doing that locally and writing out the 
entire 1G file again. About 2G of network traffic.

With rsync (don't know about rdiff-backup) IIRC there are 
combinations of options that would allow it to see the new 
modification timestamp and file size, then just copy the entire file 
without comparing it with the original. It would still be copying the 
whole gig of file, but saves reading the gig of file from the backup 
to do the compare.

--
Simon Hobson

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