Datasheet

“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 137 — #163
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3
Special Installation Procedures
To optimize the performance, the third item should be improved. For SCSI
devices, the disconnect feature comes into play. When this feature is used,
the controller sends the command Go to track x, sector y to the connected
device (in this case, the hard disk). Now the inactive disk mechanism starts
moving. If the disk is smart (if it supports disconnect) and the controller
driver also supports this feature, the controller immediately sends the hard
disk a disconnect command and the disk is disconnected from the SCSI
bus. Now, other SCSI devices can proceed with their transfers. After some
time (depending on the strategy or load on the SCSI bus) the connection to
the disk is reactivated. In the ideal case, the device will have reached the
requested track.
On a multitasking, multiuser system like Linux, these parameters can be
optimized effectively. For example, examine the excerpt of the output of the
command df in Example 3.1.
Example 3.1: Example df Output
Filesystem Size Used Avail Use% Mounted on
/dev/sda5 1.8G 1.6G 201M 89% /
/dev/sda1 23M 3.9M 17M 18% /boot
/dev/sdb1 2.9G 2.1G 677M 76% /usr
/dev/sdc1 1.9G 958M 941M 51% /usr/lib
shmfs 185M 0 184M 0% /dev/shm
To demonstrate the advantages, consider what happens if root enters the
following in /usr/src:
tar xzf package.tgz -C /usr/lib
This command extracts package.tgz to /usr/lib/package. To do
this, the shell runs tar and gzip (both located in /bin on /dev/sda) then
package.tgz is read by /usr/src (on /dev/sdb). Finally, the extracted
data is written to /usr/lib (on /dev/sdc). Thus, the positioning as well
as the reading and writing of the disks’ internal buffers can be performed
almost concurrently.
This is only one of many examples. As a general rule, if you have several
hard disks (with the same speed), /usr and /usr/lib should be placed
on separate disks. /usr/lib should have about seventy percent of the ca-
pacity of /usr. Due to the frequency of access, / should be placed on the
disk containing /usr/lib.
137SUSE LINUX Enterprise Server