[Beowulf] Building a new cluster - seeking some advice

Robert G. Brown rgb at phy.duke.edu
Sat Dec 22 07:20:24 PST 2007

On Sat, 22 Dec 2007, Jeffrey B. Layton wrote:

> Robert G. Brown wrote:
>> On Sat, 22 Dec 2007, Jeffrey B. Layton wrote:
>>> very small swap file on the thumb drive if you think you need it). There 
>>> is work
>>> afoot in the Linux kernel to allow real swapping over the network. It's 
>>> not quite
>>> there yet (the last I looked), but it does look like Linus will allow it 
>>> once it's
>>> reaches some level of maturity.
>> I looked at this a LONG time ago (back when I was running diskless nodes
>> out of sheer necessity because the nodes we got as part of a giveaway
>> program had an unsupported SCSI controller).  There was a "move afoot"
>> then, too, but this was maybe 2000.  So don't hold your breath.
> http://lwn.net/Articles/262379/
> http://kerneltrap.org/Linux/Swap_Over_NFS
> http://kerneltrap.org/Linux/Memory_Management_Improvements

Yeah, all that stuff.  Memory management, locking, page sizes, slow, and
if you pushed it it could lock up your system, but maybe adequate to
keep your system from locking up if you run barely over, rarely.

I personally hope they do it, although I do think that we're about to go
through yet another paradigm shift.  With flash coming down to around
$10/GB or less wholesale in sizes up to 16 GB, I think we'll start
seeing pure flash-boot systems appear any day now.  As in systems with
built-in 4 GB flash memory holding the basic OS installation, systems
with 8 GB flash memory holding the OS and several GB of userspace.  A
whole new kind of thin.

Built in would have certain advantages -- USB fobs are too easy to knock
off and are regrettably slow.  For clusters I'm not sure -- they are
quite slow compared to disk, and even slow compared to network disk.
Too slow?  For loading/reading they're not so bad, and Linux will get
the pages into memory if there is enough memory and work no better or
worse than network diskless.

The diffentiation then is management.  I'm not convinced that it will be
easier to install and manage a cluster with (say) 1 to 4 GB flash drives
used as boot compared to using e.g. warewulf to manage boot images.  Or
that it will be faster.  Or (really) cheaper -- $40 is still $40 more
than a diskless system, and $40 that would buy it more real memory that
is likely to ultimately be more valuable in terms of improved
performance and stability.


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Robert G. Brown                            Phone(cell): 1-919-280-8443
Duke University Physics Dept, Box 90305
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