Re: [Moosefs-users] Write starvation

[Ricardo J. B. <ric...@da...>]

El Miércoles 29 Junio 2011, Robert escribió:
> Yes, we use Centos, but installing and using the ktune package generally
> resolves most of the performance issues and differences I have seen with
> Ubuntu/Debian.

Nice to know about ktune and thank you for bringing it up, I'll take a look a 
it.

> I don't understand the comment on hitting metadata a lot? What is a lot?

A lot = reading / (re)writing / ls -l'ing / stat'ing too often.

If the client can't cache the metadata but uses it often, that means it has to 
query the master every time.

Network latencies might also play a role in the performance degradation.

> Why would it make a difference? All the metadata is in RAM anyway? The
> biggest limit to speed seems to be the number of IOPS that you can get out
> of your disks you have available to you. Looking up the metadata from RAM
> should be several orders of magnitude faster than that.

Yep, and you have plenty of RAM, so that shouldn't be an issue in your case.

> The activity reported through the CGI interface on the master is around
> 2,400 opens per minute average. Reads and writes are also around 2400 per
> minute alternating with each other. mknod has some peaks around 2,800 per
> minute but is generally much lower. Lookup's are around 8,000 per minute
> and getattr is around 700 per minute. Chunk replication and deletion is
> around 50 per minute. The other numbers are generally very low.

Mmm, maybe 2 chunkservers are just too litle to handle that activity but I 
would also check the network latencies.

I'm also not really confident about having master and cunkserver on the same 
server but I don't have any hard evidence to support my feelings ;)

> Is there a guide/hints specific to MooseFS on what IO/Net/Process
> parameters would be good to investigate for mfsmaster?

I'd like to know that too!

Cheers,
-- 
Ricardo J. Barberis
Senior SysAdmin / ITI
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