Questions[multiplexing](server)

I just found out about the ControlMaster/ControlPath feature of OpenSSH, which allows you to use a single SSH connection to run multiple terminals.

As I often use SSH to use port forwarding to get encrypted and authenticated VNC sessions I instantly recognized that you can't add port forwardings to a remote server to which you already have an established connection. This sucks.

Sometimes later I found out that you can circumvent this limitation by typing ~C in a running SSH terminal session. This opens up a command-line which allows you to add or remove port forwardings.

My quesion now is: How can I add port forwardings on an existing SSH session which is using the ControlMaster/ControlPath feature, without the need to have access to a terminal session inside that SSH session. I need this to enable my script which starts a secure tunneled VNC connection for me to add and later remove its port forwardings.

(I know I could use a terminal multiplexer such as GNU Screen or tmux, actually I'm doing this already. But I like the idea of using just one SSH session for serveral reasons.)

i'm studing for a multimedia networks exams and i don't understand why ATM is asynchronous. i know that it is asyncrhonous if used with SONET but this makes no sense..

On our Repository server adding a ControlMaster to the ssd/config file (creates socket?) resulted in a 50x transfer speed increase from roughly 2.5 seconds averaged to 0.05 seconds average. The transfer speed is between the repository system and our web servers. Now I would like to apply the same performance gain to the windows -> repository connection. We currently use Tortoise to connect via SSH, and I read on wikipedia that Putty does not natively support session multiplexing. I am aware there are other SSH tools with the feature that are also made for windows, but I was wondering if using these if I would run into issues with compatibility with Mercurial using the SSH connection as right now I believe it uses Plink to handle the SSH tunneling.

I am looking for any options for enabling session multiplexing on windows that are compatible with Mercurial.

I am using the following options in my ~/.ssh/config in order to enable connection multiplexing:

ControlMaster auto
ControlPath ~/.ssh/control/master-%r@%h:%p

However, this has the annoying problem that the first shell to connect to a particular server must be the last to disconnect, because it is the master connection that all the other connections are using. So if you log out of the master, it appears to just hang. To solve this, I would like to wrap ssh with a script that checks if the control master file exists, and if not, starts a master ssh process in the background. Then it would start a slave ssh session.

In order to accomplish this, my script would have to determine the path to the control file that ssh would use. This would entail parsing the ssh command line options and config files and implementing the logic for determining the ControlPath. Is there any way to just ask ssh what path it would use, so I can check it?

My question is... what multiplexing factor in NetBackup is recommended / do you use for Oracle RMAN backups over 1Gb/s management network to LTO3?

JB

Background:

With enterprise backup tools like NetBackup, there is the concept of Multiplexing which is the combining of data from a number of backup clients simultaneously in order to feed modern high speed tape drives as quickly as possible.

The number of simultaneous client data streams interleaved is determined by the Multiplexing factor. The higher the multiplexing factor, the more data fed to the tape drive, but the slower any restores.

As overall restore speed is mostly determined by the messing about (log incident, determine if tapes are available, recall from offsite, load, inventory, etc. ) than by the actual tape restore speed, I feel confident using a high factor for filesystem backups.

Oracle backups with large datasets, which are more often restored all together, pose a different challenge to filesystem backups.