[Beowulf] Building new cluster - estimate

Matt Lawrence matt at technoronin.com
Tue Aug 5 22:37:13 EDT 2008


On Wed, 6 Aug 2008, Chris Samuel wrote:

> I suspect you're not doing a lot of disk I/O, we
> found NFS servers using ext3 as a back end would
> crumble under the weight of lots of writes as ext3
> is single threaded through the journal daemon.
>
> That means that you end up with all your NFS daemons
> blocking on that, stalling everything else. :-(

Could be.  Given the long and sordid history of NFS, I prefer to not use 
it whenever there are practical alternatives.  I'm also not a Solaris 
fanboy.  So, different mindset that a lot of unix sysadmins.

> There have been occasional bugs in XFS in older kernel
> releases, but then there have been bugs in other filesystems
> too.

That could be it, he does spend a fair amount of time cleaning up systems 
that others have built.

> Never had that problem here.
>
> Does he know that he can use xfs_fsr to defragment
> XFS filesystems online ?

He certainly does.  He was talking about using OpenNMS to determine the 
best time to run it.  He had lots of good things to say about how easy it 
is to track through performance data with it.

> Is he sure he's not hitting another kernel bug ?

It wouldn't surprise me.

This is someone who I trust enough that if he warns me of something, I 
make a real effort to doublecheck if it is currently a problem.  It 
doesn't mean he is always right, just that I think the research effort is 
a really good idea.

-- Matt
It's not what I know that counts.
It's what I can remember in time to use.
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