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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
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:
•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;
•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.”
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