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Full Discussion: About swap
Top Forums UNIX for Dummies Questions & Answers About swap Post 95088 by jim mcnamara on Friday 6th of January 2006 09:31:24 AM
Old 01-06-2006
Normally, swapfiles are allocated in the "middle" of the disk and are created so that they are pretty much contiguous.

The reason is so that the disk head, on average, will have to move the shortest distance before it hits the cylinder in the swapfile it needs.

Having the file at the beginning or end of the disk is not a big deal but it will, on average, increase seek time.

See:

http://en.wikipedia.org/wiki/Seek_time
 

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SWAPON(8)						     Linux Programmer's Manual							 SWAPON(8)

NAME
swapon, swapoff - enable/disable devices and files for paging and swapping SYNOPSIS
/sbin/swapon [-h -V] /sbin/swapon -a [-v] [-e] /sbin/swapon [-v] [-p priority] specialfile ... /sbin/swapon [-s] /sbin/swapoff [-h -V] /sbin/swapoff -a /sbin/swapoff specialfile ... DESCRIPTION
Swapon is used to specify devices on which paging and swapping are to take place. Calls to swapon normally occur in the system multi-user initialization file /etc/rc making all swap devices available, so that the paging and swapping activity is interleaved across several devices and files. Normally, the first form is used: -h Provide help -V Display version -s Display swap usage summary by device. Equivalent to "cat /proc/swaps". Not available before Linux 2.1.25. -a All devices marked as ``swap'' swap devices in /etc/fstab are made available. Devices that are already running as swap are silently skipped. -e When -a is used with swapon, -e makes swapon silently skip devices that do not exist. -p priority Specify priority for swapon. This option is only available if swapon was compiled under and is used under a 1.3.2 or later kernel. priority is a value between 0 and 32767. See swapon(2) for a full description of swap priorities. Add pri=value to the option field of /etc/fstab for use with swapon -a. Swapoff disables swapping on the specified devices and files. When the -a flag is given, swapping is disabled on all known swap devices and files (as found in /proc/swaps or /etc/fstab). NOTE
You should not use swapon on a file with holes. Swap over NFS may not work. SEE ALSO
swapon(2), swapoff(2), fstab(5), init(8), mkswap(8), rc(8), mount(8) FILES
/dev/hd?? standard paging devices /dev/sd?? standard (SCSI) paging devices /etc/fstab ascii filesystem description table HISTORY
The swapon command appeared in 4.0BSD. Linux 1.x 25 September 1995 SWAPON(8)
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