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System Disk Partitioning

The Solaris Operating Environment installation procedure offers unlimited freedom for system disk partitioning. Creating a separate file system for a directory has a fundamental disadvantage: this file system can be full while there is ample free space elsewhere on the same disk. At that point, you may regret partitioning the disk and will have to have someone correct the situation. We recommend you follow this basic rule:

Do not partition unless there is a compelling reason to do so.

This leads to the following recommended system disk partitioning at installation. (The following partition sizes are reasonable defaults for a system disk of at least 9 GB.)

0 / (recommended size + 1 GB)
1 swap (rest of the disk)
3 /var (recommended size + 2 GB)


(2 GB dedicated for crash dumps)


(30 MB reserved for the Solaris Volume Manager software state database)

/var is on a separate partition because unprivileged users can fill the /var directory in various ways that are hard to control, as shown in the following example.



/var/mail (repeat mailx root < bigfile)
/var/spool/lp (if a local printer is configured)
/var/adm/messages (repeat logger -p daemon.err "message sent on $(date)")

By separating /var from /, unprivileged users cannot write to the root file system, and can, therefore, also not fill it.

The size of the /var file system must be sufficient to hold a kernel crash dump and is, therefore, at least as large as the dedicated crash dump partition.

Partition 4 is configured as a dedicated area for kernel crash dumps. The advantage of a dedicated, unmirrored dump partition is that the crash dump does not depend on the integrity of the mirror driver at the time of the panic. An additional advantage is faster boot after a system panic. The crash dump file can be constructed from the dump device in background, without holding up the boot process.

Configure the dedicated dump device using dumpadm -d /dev/dsk/c0t0d0s4.

The swap partition absorbs all the remaining disk space. If / or /var should fill up in spite of the large margins, the swap device can be taken off-line, shrunk, and added back. The obtained disk cylinders can be used to solve the problem (for example, by creating an /opt file system).

This configuration is preferable to keeping unused spare cylinders on the disk. If these spare cylinders must later be turned into additional swap space, two swap devices are created on different locations of the same physical disk, with a negative effect on system performance.

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