Filter
Top Products
StorNext File System Tuning
The Metadata Controller System
StorNext File System Tuning Guide 19
slower CPU.) Differences in latency over time for the same system can
indicate new hardware problems, such as a network interface going
bad.
If a latency test has been run for a particular client, the cvadmin who
long command includes the test results in its output, along with
information about when the test was last run.
Mount Command
Options
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.