Bits and Chaos

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Between bits and chaos, a sysadmin stands.

LinkedIn and MTU settings for Linux systems

For reasons quite above my understanding, some (including mine) Linux systems are unable to access LinkedIn. Symptoms include hanging forever in the login page, i.e. you could access the authentication page, reading some and yours profile, but cannot do anymore.

This could fixed by issuing, as root:

ifconfig eth0 mtu 1360

(assuming that you reach the Internet via eth0).

It’s quite a strange setup, indeed. The only other time I had to do something like that was when I was trying to reach a Moodle server, that we had put on a LAN connected to the Internet via an ADSL consumer connection; the server was reachable from each customer of the same ISP but stuck for everyone else, everytime the poor guy requests a page whose size is more than or reaching the TCP/IP maximum payload (I guess this is for some kind of NAT magic/MPLS black magic/Peering sorcery that happens only for customers outside the AS).

I’m pretty sure that LinkedIn is not using a customer ADSL to connect itself to the Internet, and that they are seeing a constant loss of Linux customers due to this issue, which is very difficult to spot.

Filed under: network, , , ,

NYSE will move to Linux

NY Times reports that the New York Stock Exchange is heavily investing in Linux. Tech speaking:

  • they prefer Linux over IBM-AIX and HP-UX, and they have HP hardware (Opteron blades and Integrity);

  • they will use HP OpenView for monitoring;

  • they are already using Solaris on some systems, but prefer to move to a more open system;

  • they do not like virtualization, as it introduces not negligible latency.

Using Linux (in the Red Hat or SuSE flavor, I guess. Note that Red Hat is listed on NYSE) will be of big impact to financial institutions world-wide, as the volume of data and money processed by the NYSE is simply enormous: NYSE is saying that Linux is mature enough although is not so polyshed as other Unix dialects. Some feature are missing (as an example, backup of an entire system, a la mksysb in IBM AIX) but these things can usually be managed at the infrastructure level: if you system is completely redundant, you can put offline small portions of it and do the planned maintenance tasks. It will cost money for the redundancy (which is possible you would pay in every case) but it’s entirely possibile that it would be cheaper than paying the high licenses for other unixes, especially when, in the long term you will found yourself vendor locked-in.

Latency in virtualization is a big problem, best known as os interference (see this good article from IBM) that will severely impact performances for HPC clusters and could be desruptive for financial trading systems, where you receive hundreds of different data feeds per second, and you should decide what to buy or sell according to some heuristics before your competitors. It will be interesting to see what the Red Hat MRG platform will do in this field. As usual, we are at the beginning of the open source world.

Filed under: virtualization, , ,