[Beowulf] Striped file system with RAM disk.

Alan Louis Scheinine scheinin at crs4.it
Thu Nov 22 08:07:46 EST 2007


    There is a particular kind of application, single-client
and serial process, for which a striped file system using
RAM disk would be very useful.  Consider reading small
blocks at random locations on a hard disk.  The latency
of the HDD could be a few milliseconds.  Adding more HDD's
does not solve the problem, unlike an application based on
streaming.  Adding more disks and parallelizing the program
could be a solution but sometimes there is no time
to parallelize the program.

    A possible solution is RAM disk.  But if we put, for example,
64 GB of RAM on a single computer then that computer becomes
specialized and expensive, whereas the need for a huge
amount of RAM may be only temporary.  An alternative is to
use a cluster of nodes, a typical Beowulf cluster.  For example,
using a striped file system over 16 nodes where each node has 4 GB
of RAM.  Each node would have a normal amount of RAM and yet
could provide the aggregate storage of 64 GB when the need arises.
While we have not yet created this configuration, I suppose
that Gbit Ethernet could provide 100 microsecond latency and
Infiniband or Myrinet could provide 10 microsecond latency.
Much, much less than the seek time of a HDD.

    The idea is so simple that I imagine it has already been done.
I would be interested in learning from other sites that have
used this method with a file system such as Lustre, PVFS2 or
another.

best regards,
Alan Scheinine

-- 

  Centro di Ricerca, Sviluppo e Studi Superiori in Sardegna
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