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StorNext File System Tuning
The Metadata Controller System
StorNext File System Tuning Guide 17
Mount Command
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The following SNFS mount command settings are explained in greater
detail in the
mount_cvfs man page.
The default size of the buffer cache varies by platform and main memory
size, and ranges between 32MB and 256MB. And, by default, each buffer
is 64K so the cache contains between 512 and 4096 buffers. In general,
increasing the size of the buffer cache will not improve performance for
streaming reads and writes. However, a large cache helps greatly in cases
of multiple concurrent streams, and where files are being written and
subsequently read. Buffer cache size is adjusted with the buffercachecap
setting.
The buffer cache I/O size is adjusted using the
cachebufsize setting. The
default setting is usually optimal; however, sometimes performance can
be improved by increasing this setting to match the RAID5 stripe size.
Using a large
cachebufsize setting decreases random I/O performance
when the amount of data being read is smaller than the cache buffer size.
Buffer cache read-ahead can be adjusted with the
buffercache_readahead
setting. When the system detects that a file is being read in its entirety,
several buffer cache I/O daemons pre-fetch data from the file in the
background for improved performance. The default setting is optimal in
most scenarios.
The
auto_dma_read_length and auto_dma_write_length settings determine
the minimum transfer size where direct DMA I/O is performed instead
of using the buffer cache for well-formed I/O. These settings can be
useful when performance degradation is observed for small DMA I/O
sizes compared to buffer cache.
For example, if buffer cache I/O throughput is 200 MB/sec but 512K
DMA I/O size observes only 100MB/sec, it would be useful to determine
which DMA I/O size matches the buffer cache performance and adjust
auto_dma_read_length and auto_dma_write_length accordingly. The lmdd
utility is handy here.
The
dircachesize option sets the size of the directory information cache on
the client. This cache can dramatically improve the speed of readdir
operations by reducing metadata network message traffic between the
SNFS client and FSM. Increasing this value improves performance in
scenarios where very large directories are not observing the benefit of the
client directory cache.