Linux - Performance

Howto: determine LVM device in iostat output

ls -l /dev/mapper/*

the device minor number corresponds to the dm-N number

Memory

Because the kernel does file caching the 'free' for 'buffers/cache' is actually what is available for use.

$ free -m
total used free shared buffers cached
Mem: 4096 3757 338 0 869 1814
-/+ buffers/cache: 1074 3021
Swap: 4095 0 4095

Never look at the ouput from a single vmstat, those are averages over time and do not reflect current values.

$ vmstat 1 3

sar

Memory:	$ sar -r
Swap:	$ sar -W
Paging:	$ sar -B
Queue length and load average:	$ sar -q
CPU utilization:	$ sar -u
Per-processor:	$ sar -P {cpu_num} or $ sar -P ALL
Context switching:	$ sar -w
I/O rates:	$ sar -b
Per block device:	$ sar -dp
Network:	$ sar -n DEV
Historical data:	$ sar {options} -f /var/log/sa/sa{dd}

swappiness

View/adjust kernel tendency to swap (larger is greater tendency).

To view:

cat /proc/sys/vm/swappiness

Adjust on the fly:

echo {number} > /proc/sys/vm/swappiness

Adjust permanently:

Change/set value for vm.swappiness in /etc/sysctl.conf

Issue command sysctl -p