ADSM-L

Re: network data throughput

1999-10-27 21:34:03
Subject: Re: network data throughput
From: Joerg Pohlmann <jpohlman AT CA.IBM DOT COM>
Date: Wed, 27 Oct 1999 18:34:03 -0700
What you are seeing in the stats for network data rate is the rate at which
the client is able to have data accepted by the communications method. So,
depending what's happening on the client and the speed of the network, the
statistic may be more or less accurate during backup. For restore, it is
pretty close to the truth. But coming back to backup, if the file system is
large and very little data has changed, you may find phenomenal data rates.
For example, I use a Laptop and am telephone line connected. My client
rummages through a relatively large number of files, and while rummaging,
only occasionally finds a file to send to the server. In my case, the
communications method is TCPIP and it buffers data extremely well. So, I
see an amazing speed for a telephone line, totally out of whack with
reality. What's closer to the truth is the aggregate data rate in my
summary. If you are sending large quantities of data such that the
communications method is not able to buffer spurious chunks of data, the
network data rate comes closer to the truth. Do a selective backup of large
amounts of data, especially with large files, and the data rate comes
closer to the hardware capabilities. For network speeds, expect reasonable
overheads that will result in not being able to make use of 100% of the
theoretical bandwidth available. So, for 10baseT, expect data rates in the
700-900KB/sec range, for 100baseT, 6-8 MB/sec is a reasonable expectation,
for 16mbTR, expect 1.2-1.4MB/sec, for a telephone line at "56kb", anything
in the range of 2-4KB/sec should make you happy. With Gbit EN, the network
is usually not a constraint and other server or client bottlenecks show up
(non-3590E tape drive environment, slow server CPUs, slow client CPUs,
non-ESS or non-SSA disks on either client or server, etc.). Here is my NT
client summary from last night's backup to an OS/390-based ADSM server 3000
miles away, via phone line:

Total number of objects inspected:   50,679
Total number of objects backed up:      187
Total number of objects updated:          6
Total number of objects rebound:          0
Total number of objects deleted:         11
Total number of objects failed:           6
Total number of bytes transferred:     6.47 MB
Data transfer time:                    0.17 sec
Network data transfer rate:        39,030.48 KB/sec
Aggregate data transfer rate:          1.86 KB/sec
Objects compressed by:                   51%
Elapsed processing time:           00:59:27

Hope this helps remove the mystery.

Joerg Pohlmann

"Van Ruler, Ruud R SSI-TSEA-332" <Ruud.R.vanRuler AT IS.SHELL DOT COM> on 99 10 
27
00:36:56

Please respond to "ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU>

To:   ADSM-L AT VM.MARIST DOT EDU
cc:
Subject:  network data throughput




ADSM guru's

Could someone explain me the real network data throughput (without
compression) of the a ADSM connection?

e.g.
18-10-1999 23:01:42   ANE4966I (Session: 327, Node: RIJSAP90)  Network data

                       transfer rate:        34,935.96 KB/sec

Please observe :

Our server is connected with a 100 Mb/s (Mega bit) connection. This is 100
Mb per sec!
Now since there are 8 bits in a Byte this means that the transfer rate of
the link is 100/8 = 12.5 MB/s (Byte)
Or  12,800.00 KByte (The multiplying factor for network data is 1024
instead
of 1000, but the link is based on 1000 so there are a few minor errors in
the computations.)

Now let's compare this theoretical maximum to reality shall we.

Theoretical maximum             12,800.00 KB/sec         43.9 GB/Hour
Practical reality                        10,000.00 KB/sec        34.3
GB/Hour
in our example                  34,935.96 KB/sec        119.9 GB/Hour

As you can see, the  values greatly exceed the theoretical maximum.
How is this possible?
or do we misinterpreted "Network data transfer rate: 34,935.96 KB/sec" ?

thanks in advance


=======================================================
             Ruud van Ruler
Shell Services International BV - TSEA-332
Our Data Storage Management home page: http://sww2.shell.com/dstorage/
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