[syslinux] Does pxelinux tftp support BLOCK-SIZE option

[H. Peter Anvin]

Sowmya.Krishnaswamy at nokia.com wrote:
> Hello,
> 
> We are using PXELINUX to get the diskless clients up using PXELINUX as boot loader for network boot. The size of the root file system in our case is 14MB and it is taking around 15-20 minutes to get the box up which we need to bring down to 5 minutes, hence the query on TFTP BLOCK SIZE option. 
> 
> Since PXELINUX does not support TFTP BLOCKSIZE option does it imply that the root file system should be lot smaller. The maximum reduction in our case would result is something that is 10MB not less. 
> 

I would start by investigating your TFTP server.  It should not take
anywhere near that amount of time.  You don't say what tftp server
you're using, but the tftp server can make a substantial different in
the performance.  Keep in mind that given your numbers -- 14 MB in 5
minutes -- corresponds to a bandwidth requirement of 400 kbit/s *PER
CLIENT*.  If you have 250 clients that's saturating a 100 Mbit/s link,
and that's assuming there are no other traffic or bottlenecks in that
system.

Another thing that you may want to consider is using a two-stage
download process (download the kernel and a small initrd via TFTP, then
use that initrd to download the rest via NFS or HTTP.)

blksize helps you if you're latency bound only.  If you do, you probably
have a specific reason why you're booting your clients over a
high-latency link, and you're still better off investigating the
two-step boot solution, so you can use TCP.

	-hpa