Andrew Clegg's questions

What do I need to do to get LatencyTop working on Centos 6.2?

Does it involve compiling a debug kernel with some extra flags?

Both the man page and the website are very short of information.

Thanks!

EDIT: I should have been more specific, sorry, my bad. I've installed it fine from an rpm. But apparently the stock Centos 6.2 kernel doesn't support it:

mount: none already mounted or /sys/kernel/debug/ busy
mount: according to mtab, none is already mounted on /sys/kernel/debug
Xlib:  extension "RANDR" missing on display "localhost:10.0".
The running kernel does not support latencytop. Please use kernel-debug.

No idea how to install and use kernel-debug safely though, if this is the only extra thing that needs to be done. Does anyone have any pointers?

Thanks again.

I'm planning to set up a small Hadoop cluster where the slave nodes boot and run from a central PXE server, to simplify deployment and updates, and to enable all of the disks on the slaves to be (almost) monopolized by HDFS.

However, I suppose I'll still have to reserve some space on the slave nodes for /tmp and /var/log, I don't want to just put these in a ramdisk because I'd like them there for debugging after crashes (and because RAM is scarcer than disk).

So the machines might boot off the remote PXE server, mount their / read-only from there, then mount /dev/sda1 through sdd1 for the HDFS data partitions, /dev/sda2 for /tmp, and /dev/sdb2 for /var/log.

My question is, are there any other directories that will need to be writable? Assuming we get Hadoop etc. to log into /var/log.

(And is this a sensible architecture in general?)

EDIT: don't worry about swap, I'm planning to make these swapless, the OOM killer is preferable to thrashing.

We have a CentOS 5.5 KVM host, running guests with various versions of CentOS and possibly other OSes later.

We'd like to be able to either (a) automatically send an ACPI shutdown to all guests or (b) suspend all guests to disk, on host shutdown.

Is there a standard method to accomplish either of these, or is it a roll-your-own situation? Thanks!

We're interested in restricting the number of requests per second and/or available bandwidth to HTTP clients, to stop accidental DoS. We provide free scientific data and web services, and sadly some users' scripts aren't well behaved.

I know there's lots of Apache mods that allow you to throttle per client IP address, but the problem is, sometimes we see people doing distributed crawling from their clusters (today this caused a load average > 200 incident!).

What I'd really like to do is throttle per /24 subnet, but without having to specify which subnets in advance.

Ideally, I'd also like to be able to do this as a proportion of a maximum cap, so if we're only seeing requests from one subnet, they get to use all the server's resources, but if two subnets are competing, they get to use half each.

Is this possible with either:

• Apache mods
• Traffic control
• Proxy server
• Something else?

Thanks!

EDIT: Couple of further things... If anything needs to be done at the network infrastructure level (e.g. routers) that's out of our responsibility and becomes an instant PITA. So I'm hoping to find a solution that only requires changes at the server level. Also please don't be offended if I take a while to pick a winner, this is a new topic to me so I want to read around the suggestions a bit :-)