[Lustre-discuss] ram disk

[Antonio Concas]

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 large, 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 the Lustre file system.

best regards,