| Bill Todd 2007-04-02, 1:14 pm |
| markm75 wrote:
....
> This baffles me.. as I know that I can do the backup on the same drive
> locally in 4 hours on that machine.. and I know I can do the same type
> backup on the remote (destination) as well.. so going from D on
> ServerA to E on ServerB should just be a limitation of the network,
> which benches at 60 MB/s in all of my tests.
While I have no specific solution to suggest, it is possible that the
problem is not network bandwidth but network latency, which after the
entire stack is taken into account can add up to hundreds of
microseconds per transaction.
If the storage interactions performed by the backup software (in
contrast to simple streaming file copies) are both small (say, a few KB
apiece) and 'chatty' (such that such a transaction occurs for every
modest-size storage transfer) this could significantly compromise
network throughput (since the per-transaction overhead could increase by
close to a couple of orders of magnitude compared to microsecond-level
local ones).
Another remote possibility is that for some reason transferring across
the network when using the backup software is suppressing write-back
caching at the destination, causing a missed disk revolution on up to
every access (though the worst case would limit throughput to less than
8 MB/sec if Windows is destaging data in its characteristic 64 KB
increments, and you are apparently doing somewhat better than that).
- bill
|