20 Apr
2010
20 Apr
'10
9:48 p.m.
I'm a student and work at a school where we image our machines using
UDPcast. It has been a great tool for installing entire classrooms quickly,
but we recently upgraded all of our hardware and are now running gigabit
ethernet. We've configured the eth0 to have an MTU of 9000 with the
following line
ifconfig eth0 mtu 9000
on both the sending and receiving computers. After preparing the machines we
use the udp-sender command to copy the master hard drive over the network
and include the switch
--blocksize=9000
but it doesn't seem to affect our transfer speeds at all. Without changing
the MTU or blocksize it sends at around 180 Mbps and after changing the MTU
and blocksize it still sends at about the same speed. Is there possibly
another bottleneck we've overlooked such as bus speeds or hard drive
transfer speeds? Or does UDPcast not support jumbo frames? I saw somewhere
in the archives that the blocksize can be reduced if your network doesn't
support 1500 byte frames, but never anything about increasing the size.
Please advise, thank you very much!
21 Apr
21 Apr
2:07 a.m.
What are the true speeds of the hard disks?
You are only looking at the network speed, but the data also needs to be
written to the disk, and disk imaging does massive disk access, so the hard
disk buffer is quickly used up.
If you can, run hdparm -Tt /dev/sda (or whatever the disk is)
That will report to you the disk speed using the buffer and not.
On the machine I am using at the moment.
/dev/sda:
Timing cached reads: 4898 MB in 2.00 seconds = 2450.11 MB/sec
Timing buffered disk reads: 254 MB in 3.01 seconds = 84.46 MB/sec
In the past, I had show students how using 100MB nics we could get an over
speed of about 30MB/sec. After putting 1GB nics in two machines, the same
transfer gave about 65MB/sec. The nic was 10 times faster, but now the
hard disk was the limiting factor.
On 20 Apr 2010 at 11:48, Michael Gunter wrote:
Date sent: Tue, 20 Apr 2010 11:48:14 -1000
From: Michael Gunter <vir.iratus1686(a)gmail.com>
To: udpcast(a)udpcast.linux.lu
Subject: [Udpcast] Jumbo Frames in UDPcast?
I'm a student and work at a school where we image our machines using UDPcast. It has
been a
great tool for installing entire classrooms quickly, but we recently upgraded all of our
hardware
and are now running gigabit ethernet. We've configured the eth0 to have an MTU of
9000 with
the following line
ifconfig eth0 mtu 9000
on both the sending and receiving computers. After preparing the machines we use the
udp-
sender command to copy the master hard drive over the network and include the switch
--blocksize=9000
but it doesn't seem to affect our transfer speeds at all. Without changing the MTU or
blocksize it
sends at around 180 Mbps and after changing the MTU and blocksize it still sends at about
the
same speed. Is there possibly another bottleneck we've overlooked such as bus speeds
or hard
drive transfer speeds? Or does UDPcast not support jumbo frames? I saw somewhere in the
archives that the blocksize can be reduced if your network doesn't support 1500 byte
frames,
but never anything about increasing the size. Please advise, thank you very much!
+----------------------------------------------------------+
Michael D. Setzer II - Computer Science Instructor
Guam Community College Computer Center
mailto:mikes@kuentos.guam.net
mailto:msetzerii@gmail.com
http://www.guam.net/home/mikes
Guam - Where America's Day Begins
+----------------------------------------------------------+
http://setiathome.berkeley.edu (Original)
Number of Seti Units Returned: 19,471
Processing time: 32 years, 290 days, 12 hours, 58 minutes
(Total Hours: 287,489)
BOINC@HOME CREDITS
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ROSETTA 1882529.685530 | ABC 728490.575656
8:21 a.m.
On 20/04/10 23:48, Michael Gunter wrote:
I'm a student and work at a school where we image
our machines using
UDPcast. It has been a great tool for installing entire classrooms quickly,
but we recently upgraded all of our hardware and are now running gigabit
ethernet. We've configured the eth0 to have an MTU of 9000 with the
following line
ifconfig eth0 mtu 9000
on both the sending and receiving computers. After preparing the machines we
use the udp-sender command to copy the master hard drive over the network
and include the switch
--blocksize=9000
Just one remark: each frame has a certain amount of "overhead" (Udpcast
headers, IP headers, Ethernet headers), so in order to avoid
fragmentation (and performance loss), you need to stay slightly under
your MTU.
So, for example:
--blocksize 8952
but it doesn't seem to affect our transfer speeds at all. Without changing
the MTU or blocksize it sends at around 180 Mbps and after changing the MTU
and blocksize it still sends at about the same speed. Is there possibly
another bottleneck we've overlooked such as bus speeds or hard drive
transfer speeds? Or does UDPcast not support jumbo frames? I saw somewhere
in the archives that the blocksize can be reduced if your network doesn't
support 1500 byte frames, but never anything about increasing the size.
Please advise, thank you very much!
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Udpcast(a)udpcast.linux.lu
https://udpcast.linux.lu/cgi-bin/mailman/listinfo/udpcast
Regards,
Alain
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days inactive
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2 comments
3 participants
participants (3)
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Alain Knaff -
Michael D. Setzer II -
Michael Gunter