Lustre
Lustre metrics are enabled if your compute nodes have one or more Lustre filesystems mounted. Lustre metrics are obtained from a Lustre client process running on each node. Therefore, the data presented gives the information gathered on a per-node basis. The data presented is also cumulative over all of the processes run on a node, not only the program being profiled. Therefore, there might be some data reported to be read and written even if the program itself does not perform file I/O through Lustre.
However, an assumption is made that the majority of data read and written through the Lustre client is from an I/O intensive program, not from background processes. This assumption has been observed to be reasonable. For generated program profiles with more than a few megabytes of data read or written, almost all of the data reported in Linaro MAP is attributed to the program that is profiled.
The data that is gathered from the Lustre client process is the read and write rate of data to Lustre, as well as a count of some metadata operations. Lustre does not just store pure data, but associates this data with metadata, which describes where data is stored on the parallel file system and how to access it.
This metadata is stored separately from data, and needs to be accessed whenever new files are opened, closed, or files are resized. Metadata operations consume time and add to the latency in accessing the data.
Therefore, frequent metadata operations can slow down the performance of I/O to Lustre. Linaro MAP reports on the total number of metadata operations, as well as the total number of file opens that are encountered by a Lustre client. With the information provided in Linaro MAP, you can observe the rate at which data is read and written to Lustre through the Lustre client. You can also identify whether a slow read or write rate can be correlated to a high rate of expensive metadata operations.
Note
For jobs run on multiple nodes, the reported values are the mean across the nodes.
If you have more than one Lustre filesystem mounted on the compute nodes the values are summed across all Lustre filesystems.
Metadata metrics are only available with Linaro Forge Ultimate.
- Lustre read transfer
The number of bytes read per second from Lustre.
- Lustre write transfer
The number of bytes written per second to Lustre.
- Lustre file opens
The number of file open operations per second on a Lustre filesystem.
- Lustre metadata operations
The number of metadata operations per second on a Lustre filesystem. Metadata operations include file open, close, and create, as well as operations such as readdir, rename, and unlink.
Note
Depending on the circumstances and implementation, file open might count as multiple operations. For example, this might happen when a file open creates a new file or truncates an existing one.