> Hello All,
> We are testing out the use of SUBFILE processing. We have a user
> group that would have to do dial-in backups or we buy them zip drives.
> Using SUBFILE processing, a very narrow include/exclude list, and
> compression we still se backups that are close to 40MB. We insist that the
> test group get a connection of at least 40K bits/sec. I see the backups
> running at less than 2K bytes/sec. I played with many different parms and
> can not get things to run any faster. If this is the best we can do we will
> be purchasing a lot of zip drives (400+). HAS ANYONE ELSE TRIED THIS? IS
> ANYONE ELSE GETTING BETTER THROUGHPUT ON A 56kbs DIALUP line?
Matt - Two points on this issue...
1. There's no such thing as a 56kbs dialup line, which is to say that the
phone company does not (refuses to) guarantee voice lines for data,
and certainly no guaranteed speed. You get whatever the line conditions
will tolerate at the moment. I've tried a 56K modem at home and found
that the line conditions made high-speed connections so error-dominated
that throughput was worse than using a slower modem. I returned to using
a 28.8 modem, and even there have to limit it to 26.4 kbps to achieve
best possible throughput.
2. The term "56K modem" is too loosely thrown around. The technology does
not provide 56Kbps capability in both directions. From my notes:
56Kb (V.90) modems V.90 bypasses the normal
digital-to-analog conversion on
downloads, so maximizes line
utilization. Full telco line capacity is
53Kbps. Although most standard,
voice-grade phone lines can carry 56Kbps
of digital data, telephone companies
have traditionally used only about 53Kb
of that in order to provide some quiet
buffer space between adjacent voice
channels in their analog world. Now that
most phone systems are all digital, that
3Kb of quiet space is no longer
necessary, so the FCC lifted the 53Kb
limit. The upload side of the line is
still based upon digital-to-analog
conversion, so is limited to 33Kbps.
Lastly, regarding the large backups you are still seeing, I would advise
reading the whitepaper on Adaptive Sub-file Differencing at
http://www.tivoli.com/products/solutions/storage/storage_related.html .
There are circumstances under which full backups need to occur. The scheme
is not magic.
Richard Sims, BU
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