Re: rsync over ssh/nfs (was: server crashing)

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Thu, Sep 01, 2011 at 07:30:21AM +0200, Niels Dettenbach (Syndicat 
IT&Internet) wrote:
> 
> David Brownlee <abs%netbsd.org@localhost> schrieb:
> >As an aside I've found rsync over NFS substantially faster than over
> >ssh for
> >large files on lowish (HP microserver amd64) spec boxes.
> 
> This is to expect as a SSH connection by principe adds much more processing 
> overhead (crypto, TCP) then a typical NFS connection.

No, it is *not*.   Using rsync "over NFS" is tantamount to not using
rsync at all, since the entire file contents flow over the network.

The only cases in which it should actually be faster are if there
are very many files and almost no changes (per-file latency will
dominate the total cost, and stat() over NFS is probably faster
than stat()-by-proxy-between-two-copies-of-rsync-over-SSH) or if
the files are very large and almost their entire contents have
changed.

Otherwise, the entire *point* of rsync is to *not* transfer the
entire data of the file over the network, and running rsync over
NFS entirely defeats that, since to checksum the hunks of the file
the entire file must be read over NFS...which is to say, over the
network!

Thor