Quantum 6-01376-07 manual StorNext File System Tuning Metadata Controller System

StorNext File System Tuning

The Metadata Controller System

The “PERF: VFS” trace shows throughput measured for the read or write system call and significant aspects of the I/O, including:

•Dma: DMA

•Buf: Buffered

•Eof: File extended

•Algn: Well-formed DMA I/O

•Shr: File is shared by another client

•Rt: File is real time

•Zr: Hole in file was zeroed

Both traces also report file offset, I/O size, latency (mics), and inode number.

Sample use cases:

•Verify that I/O properties are as expected.

You can use the VFS trace to ensure that the displayed properties are consistent with expectations, such as being well formed; buffered versus DMA; shared/non-shared; or I/O size. If a small I/O is being performed DMA, performance will be poor. If DMA I/O is not well formed, it requires an extra data copy and may even be broken into small chunks. Zeroing holes in files has a performance impact.

•Determine if metadata operations are impacting performance.

If VFS throughput is inconsistent or significantly less than Device throughput, it might be caused by metadata operations. In that case, it would be useful to display “fsmtoken,” “fsmvnops,” and “fsmdmig” traces in addition to “perf.”

•Identify disk performance issues.

If Device throughput is inconsistent or less than expected, it might indicate a slow disk in a stripe group, or that RAID tuning is necessary.

•Identify file fragmentation.

If the extent count “exts” is high, it might indicate a fragmentation problem.This causes the device I/Os to be broken into smaller chunks, which can significantly impact throughput.