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nswapdev.5 (2010 09)

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nswapdev(5) nswapdev(5)
(Tunable Kernel Parameters)
NAME
nswapdev - maximum number of devices that can be enabled for swap
VALUES
Default
32 devices
Allowed values
Minimum:
1 device
Maximum:
1024 devices
DESCRIPTION
Swap devices are managed in a table for easier indexing in the kernel.
nswapdev sets the kernel vari-
able responsible for the upper limit on this table, and thus the upper limit to devices which can be used
for swap.
Who is Expected to Change This Tunable?
Anyone.
Restrictions on Changing
Changes to this tunable take effect at the next reboot.
When Should the Value of This Tunable Be Raised?
If another swap device is added to the system which would increase the number of devices above
nswap-
dev, and swapon() returns [ENOENT] to the caller (see the swapon (2) manpage).
What Are the Side Effects of Raising the Value?
More devices can be added to the system, and the kernel will need a little more memory for the table. A
small performance side effect of the kernel having to scan more devices to check for a duplicate device
during
swapon is also true, but realistically negligible.
When Should the Value of This Tunable Be Lowered?
Only if you are sure the system will never go over a certain number of swap devices, and you wish to
lower this tunable to save a small amount of kernel memory and kernel performance during
swapon
operations.
What Are the Side Effects of Lowering the Value?
No side effects other than the primary and presumably desired new limitation on the number of swap
devices.
What Other Tunable Values Should Be Changed at the Same Time?
None.
WARNINGS
All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its
meaning changed in future releases of HP-UX.
Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parame-
ter values. After installation, some tunable parameters may no longer be at the default or recommended
values. For information about the effects of installation on tunable values, consult the documentation for
the kernel software being installed. For information about optional kernel software that was factory
installed on your system, see HP-UX Release Notes at
http://www.hp.com/go/hpux-core-docs
.
AUTHOR
nswapdev was developed by HP.
SEE ALSO
kctune(1M).
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

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