Memory and Disk Utilization

Memory Utilization

Type	total	free	used	percent	shared	buffers	cached
				%

Disk Utilization

Mount	Disk	Size	Free	Used	Precent	Type
/	/dev/hda1	189.76 GByte	21.48 GByte	168.28 GByte	89%	xfs
/mnt	/dev/hdb1	189.76 GByte	70.53 GByte	119.23 GByte	63%	xfs
/dev/shm	tmpfs	1012.50 MByte	1012.50 MByte	0.00 Byte	0%	tmpfs
/tmp	tmpfs	1012.50 MByte	1012.34 MByte	172.00 kByte	1%	tmpfs

Memory is an important resource for the overall performance of a server system. Too little memory will cause the server to have to use the much slower disk system to temporarily store programs that are executing whenever a higher-priority task requires the use of memory. Therefore, while having 1 Gbyte or more of memory is good, it is the percentage of that memory that is being used that is important.

In the memory table above, any time the memory usage goes above 80 percent, the indicator bar will turn red; otherwise, the bar will be green. The memory figures are a measure taken at a recent point in time. The "mem" figures are for the main system memory. The "swap" figures refer to the disk area set aside for memory swapping, used when more memory is needed and none is available. Inactive memory pages are written out to disk and their memory freed for use by higher-priority programs. Since this process effectively halts the execution of the running programs while the memory is swapped, it has the effect of slowing the response of the system to user requests. Therefore, swap utilization is a measure of how much memory has been overcommitted at any one time.

Disk space utiliization will measure how full the drives on the system are getting. If you're on a shared host (most likely), then you'll want this to be less than 80 percent. The indicator bar will change color to red if disk free space falls below 20 percent. A higher number may indicate that too many virtual hosts have been placed on this system, and the users are filling up the drives with their web site pages. A highly-utilized drive will also slow down the server's access to the information on it, as it works to respond to each request by thrashing around the disk looking for the required disk block.