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Dell Storage for HPC with Intel Enterprise Edition for Lustre sofware
Figure 11: N-to-1 IOR Read / Write
4.4 Metadata Testing
Metadata testing measures the time to complete certain file or directory operations that return
attributes. MDtest is an MPI-coordinated benchmark that performs Create, Stat, and Remove
operations on files or directories. This study used MDtest version 1.9.3. The MPI stack used for this
study was Intel MPI version 5.0 Update 1. The metric reported by MDtest is the rate of completion in
terms of operations per second (OP/sec). MDtest can be configured to compare metadata performance
for directories and files. For this test, we perform a pass with file operations, then a separate pass
with directory operations.
On a Lustre file system, OSTs are queried for object identifiers in order to allocate or locate extents
associated with the metadata operations. This interaction requires the indirect involvement of OSTs in
most metadata operations. In lab experiments with the test bed, it was found that using OST count of 1
was more efficient for most metadata operations, especially for higher thread counts. The experiments
consisted of conducting tests with up to 64 clients for the following Lustre topologies (results not
presented here), to select the most efficient configuration for the metadata performance tests for this
version of the solution:
 1 OST, 1MB Stripes
 1 OST, 4MB Stripes
 24 OSTs, 1MB Stripes
 24 OSTs, 4MB Stripes
The most efficient configuration was found to be with 1 OST with 1MB stripes, therefore the results
presented in this section are with such Lustre topology.
Also during the preliminary metadata testing, it was found that the number of files per directory
significantly affects the results, even while keeping constant the total number of files created. For