[Casper] Master Image Creation Checklist

[Philip Cummins]

Hello,

> AFP throughput drops tremendously when you have tons of unicasting  
> connections that are pulling down packages at different times.   
> Package based deployment is really nice and I love it, but when you  
> are going to image thousands of machines at once you can chop off  
> minutes per a machine by doing a larger block copy of a complete  
> image.

AFP suffers massive penalties the more connections and more file  
accesses you do (DMG's are usually OK if you have good FS caches, but  
lots of small files will punish). If the network is set up properly  
multicasting can do effectively 1 to thousands of computers without  
too much of a problem. We blast over 17 GiB (compressed) to about 40  
computers at a time and it will finish in a guaranteed 40 or so  
minutes (we could probably trim it down to 35 or 30 minutes if we push  
the data rate but you can run the risk of packet loss). Our main  
limiting factor is space to set up laptops with power/connectivity for  
NetBoot. Adding additional switches for 20+ laptops at a time is not a  
problem except for NetBoot (if I make a custom MC image that would  
work OK). Cisco switches require IGMP snooping and the querier running  
to handle clients joining and leaving the multicast network properly.  
In addition the port interfaces require igmp snooping on tcn flood to  
be disabled so if new clients join/connect to the port they don't get  
swamped with packets of multicast data, esp if you mix 10/100 and  
Gigabit devices. In a controlled network this should be possible (ie,  
private network + switches), otherwise some work will be needed to  
support it on the internal networks as people mention. Testing is  
essential, you can easily start getting hundreds of MB's a second  
going over multicast if you have multiple images running  
simultaneously which can hammer a Gig to 100 MBps connection easily  
when they each start going at 15+ MiB/sec.

> AFP kind of sucks in that sense.  I have yet to try out the multi- 
> casting abilities of Casper. Anyone use multi-casting with Casper?

We don't use Casper for multicasting but I'd imagine a script could be  
made after NetBoot into Casper Imaging to accept a connection to  
restore a large disk image via multicast. At the moment we use  
multicast via asr to dump the image, then restart and join Casper  
afterwards. The setup usually is to configure the server with multiple  
multicast IP's and ports (ie, 224.x.x.31:7831, 224.x.x.32:7832) in the  
asr plist configuration and adjust the multicast data rates to avoid  
packet loss. So, probably easiest to start with a unmanaged switch (or  
good quality one if you plan on multiple multicasts), private network  
+ private Gig Ethernet connection and test from there.

Philip
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