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Dell Storage for HPC with Intel Enterprise Edition 2.3 for Lustre sofware

each Virtual Disk (OST). Figure 13 below illustrates the significant advantage to sequential write

performance when write caching was disabled.

Figure 13: Storage Write Caching

However, this increase in sequential write performance is offset by a severe degradation in random

write performance when write caching is disabled. For that reason, we recommend that write caching

only be disabled in controlled environments where random write performance is less of a concern.

4.2 Random Reads and Writes

The IOzone benchmark was used to gather random reads and writes metrics. The file size selected for

this testing was such that the aggregate size from all threads was consistently 1TB. That is, random

reads and writes have an aggregate size of 1TB divided equally among the number of threads within

that test. The IOzone host file is arranged to distribute the workload evenly across the compute nodes.

The storage is addressed as a single volume with a stripe count of 1 and stripe size of 4MB. A 4KB

request size is used because it aligns with Lustre’s 4KB file system block size and is representative of

small block accesses for a random workload. Performance is measured in I/O operations per second

(IOPS)

Figure 14 shows that the random writes peak at little over 12.6K IOPS and leveling around 144 threads,

while random reads show a steady incline as threads increase. The IOPs of random reads increase

rapidly from 48 to 96 threads and again at 120 to 144 threads. As the writes require a file lock per OST

accessed, saturation is expected. Reads take advantage of Lustre’s ability to grant overlapping read

extent locks for part or all of a file.

2000

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1 2 4 8 12 16 24 32 48 64 72 96 120 128 256

Throughput in MB/s

Number of concurrent threads

Iozone Sequential I/O - Storage Write Cache Settings - Dell

Storage for HPC with Intel EE for Lustre

Write - cache disabled Read - cache disabled Write - cache enabled Read - cache enabled