Quantum 6-01376-05 User Manual

  StorNext File System Tuning

The Metadata Controller System

StorNext File System Tuning Guide

14

The 

 utility is a higher performance alternative to commands such as 

 and 

. The 

 utility achieves high performance by using threads, 

large I/O buffers, preallocation, stripe alignment, DMA I/O transfer, and 

Bulk Create. Also, the 

 utility uses the SNFS External API for 

preallocation and stripe alignment. In the directory-to-directory copy 

mode (for example, 

,) cvcp conditionally 

uses the 

 API to provide a dramatic small file copy 

performance boost. However, it will not use 

in some 

scenarios, such as non-root invocation, managed file systems, quotas, or 

Windows security. Hopefully, these limitations will be removed in a 

future release. When 

 is utilized, it significantly boosts 

performance by reducing the number of metadata operations issued. For 

example, up to 20 files can be created all with a single metadata 

operation. For more information, see the 

 man page. 

The 

 utility provides a command line tool to utilize valuable 

SNFS performance features. These features include preallocation, stripe 

alignment, and affinities. See the 

 man page.

The 

 utility is very useful to measure raw LUN performance as well 

as varied I/O transfer sizes.
The 

 utility has a special “Perf” trace flag that is very useful to 

analyze I/O performance. For example: 

cvdbset perf

Then, you can use 

to 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