[Beowulf] ramdisk with tmpfs

Orion Poplawski orion at cora.nwra.com
Thu Mar 17 13:42:14 EDT 2011


On 03/10/2011 10:16 AM, Craig Tierney wrote:
> 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).

No, don't use /dev/shm - this is a API mount for posix shared memory.  Mount 
another tmpfs somehwere else (we mount one at /tmp).  tmpfs is very nice, just 
remember that is competes with the RAM demands of your processes.

-- 
Orion Poplawski
Technical Manager                     303-415-9701 x222
NWRA/CoRA Division                    FAX: 303-415-9702
3380 Mitchell Lane                  orion at cora.nwra.com
Boulder, CO 80301              http://www.cora.nwra.com
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