[Beowulf] ramdisk with tmpfs

[Craig Tierney]

On 3/10/11 9:49 AM, Paul Van Allsburg wrote:
> Hi All,
> I want to make a ramdisk available to cluster users and I'm curious what  your experiences/suggestions might be.  I'm adding 40
> machines to a cluster that have 24 gig of ram.  I'd like to offer the option of allowing some users to be able to run a job on a
> machine with 20 gig carved out for a ram disk.
>
> The cluster is running centos 5.5 with torque&  maui.
>
> I expect the user will have to request one machine for the job and have the prologue/eplogue scripts mount&  unmount the
> ramdisk. Are there any success / horror stories that I might be enlightened by?
>
> Thanks!
> Paul
>

As far as I recall, Centos creates a ramdisk by default at /dev/shm whose
maximum size is 1/2 of available memory.  The ramdisk uses available memory
as needed, and doesn't block an application from allocating
all of memory (as long as there is nothing in the ramdisk).

So you don't have to create one.  You can leave it bigger if you want,
but what is important is that the prologue/epilogue clears out the files
left there before the next run.  You could just mount/umount one as well
if you want, as you can have multiple ramdisks mounted at one time which
all size dynamically.

Craig