Quantum 3.1.4.1 manual StorNext File System Tuning Metadata Controller System

StorNext File System Tuning

The Metadata Controller System

The cvdbset utility has a special “Perf” trace flag that is very useful to analyze I/O performance. For example: cvdbset perf

Then, you can use cvdb -gto collect trace information such as this:

PERF: Device Write 41 MB/s IOs 2 exts 1 offs 0x0 len 0x400000 mics 95589 ino 0x5

PERF: VFS Write EofDmaAlgn 41 MB/s offs 0x0 len 0x400000 mics 95618 ino 0x5

The “PERF: Device” trace shows throughput measured for the device I/O. It also shows the number of I/Os into which it was broken, and the number of extents (sequence of consecutive filesystem blocks).

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.”

StorNext File System Tuning Guide 17