[Beowulf] Should I go for diskless or not?
landman at scalableinformatics.com
Fri May 15 08:00:42 PDT 2009
John Hearns wrote:
> 2009/5/15 Joe Landman <landman at scalableinformatics.com>:
>>>> Swap is an issue. A somewhat hard to solve issue ... we'd recommend
>> actually turning off swap (and swappiness in the kernel) for diskless. Or
>> put a USB drive in each machine and swap on that, though, honestly, that is
>> as reliable as swapping over the network. E.g. don't do it.
> At the risk of boring everyone here rigid with the "SGI" word, ICE
> clusters mount swap via iSCSI.
> It seems to work - I say seems, as I've never actually looked at a
> blade doing swap in anger.
We have tried this on other units, pushing the envelope hard on swap.
What we find is, contrary to almost every distros vendors claims,
OOM-killer wakes up and goes all wild-west on you.
You never, under any circumstances, want to wake OOM-killer. You want
to back away slowly.
I see more crashed nodes with "oom" collateral damage in the logs, than
I care to admit.
> Which reminds me - I have a to-do list task which is to test the OOM
> killer on one of these blades.
> Guess I can look at it swapping at the same time as I stress it for OOM.
Oh ... a glutton for punishment ... eek!
> Two rules of thumb for swap though:
> a) provision enough RAM on ya nodes for ya code
> b) hire Samuel L Jackson to get medieval on the ass of any users dumb
> enough to run code which leaks memory
I forgot which parody of Pulp Fiction this came from ... absolutely
hilarious! I think it was a MadTV skit.
Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics LLC,
email: landman at scalableinformatics.com
web : http://www.scalableinformatics.com
phone: +1 734 786 8423 x121
fax : +1 866 888 3112
cell : +1 734 612 4615
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