Sun Java System Web Server 6.1 SP6 Performance Tuning, Sizing, and Scaling Guide

Solaris File System Tuning

This section discusses changes that can be made for file system tuning, and includes topics that address the following issues:

High File System Page-in Rate

If you are seeing high file system page-in rates on Solaris 8 or 9, you may benefit from increasing the value of segmap_percent. This parameter is set by adding the following line to the /etc/system file:

set segmap_percent=25

segmap_percent adjusts the percentage of memory that the kernel will map into its address space for the file system cache. The default value is 12; that is, the kernel will reserve enough space to map at most 12% of memory for the file system cache. On a heavily loaded machine with 4 GB of physical memory, improvements have been seen with values as high as 60. You should experiment with this value, starting with values around 25. On systems with large amounts of physical memory, you should raise this value in small increments, as it can significantly increase kernel memory requirements.

Reduce File System Housekeeping

UNIX file system (UFS) volumes maintain the time that each file was accessed. Note that the following change does not turn off the access time updates when the file is modified, but only when the file is accessed. If the file access time updates are not important in your environment, you could turn off the same by adding the noatime parameter to the data volume's mount point in /etc/vfstab. For example:

/dev/dsk/c0t5d0s6 /dev/rdsk/c0t5d0s6 /data0 ufs 1 yes noatime

Long Service Times on Busy Disks or Volumes

Sun Java System Web Server's responsiveness depends greatly on the performance of the disk subsystem. Use the iostat utility to monitor how busy the disks are and how rapidly they complete I/O requests (the %b and svc_t columns, respectively). Service times are unimportant for disks that are less than about 30% busy, but for busier disks service times should not exceed about 20 milliseconds. If your busy disks have slower service times, improving disk performance may help Sun Java System Web Server performance substantially.

Your first step should be to balance the load: if some disks are busy while others are lightly loaded, move some files off of the busy disks and onto the idle disks. If there is an imbalance, correcting it will usually give a far greater payoff than trying to tune the overloaded disks.