topic Re: Swap limit in Operating System - Linux

Swap limit

Md.Shahabuddin — Tue, 03 Apr 2007 00:23:28 GMT

Is there a limit to the amount of swap space you can configur on the system?

Re: Swap limit

Stuart Browne — Tue, 03 Apr 2007 00:46:39 GMT

It does depend on the kernel version and the arch you're using.

But let's take a RedHat document (ES4):

https://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/x8664-multi-install-guide/s1-diskpartitioning.html#S2-DISKPARTRECOMMEND

32 x 2GB = 64GB.

Re: Swap limit

Stuart Browne — Tue, 03 Apr 2007 00:50:07 GMT

.. That being said, I've got x86 systems with 4GB swap partitions, and have no trouble with them .. but I guess it's scale-of-magnatude ..

RHEL5 appears to have a multi-TB swap limit.. so, fun.. ;)

Re: Swap limit

palaniappan.sp — Tue, 03 Apr 2007 02:42:56 GMT

Hi all,
In Red Hat Enterprise Linux 2.1 there was a limitation on the partition size of 2GB for each swap space. This was due to the mkswap command not supporting creation of a swap partition larger than 2GB. If the system requires more than 2GB of swap space, work around this limitation by creating multiple swap partitions.
RHEL3 and above, the mkswap command allows the creation of a swap partition of a larger size than 2GB.RHEL 2.1 supports upto 32 swap partitions, each can be a maximum size of 2GB. Maximum total swap size is 64GB.
RHEL3 and higher supports larger swap partitions, each can be of maximum size set by the file size limit and the block device limit for swap partitions on that platform. Red Hat Enterprise Linux 3 has a 1TB limitation as maximum size of block devices, so it's 1TB.
While larger swap partitions are permitted, one large swap partition could affect system performance. For better performance it is recommended to split swap space to multiple discs. Separating swap partitions to different disk could reduce the load on a single disk.

Let me know if any details req...

Regds,
palani.

Re: Swap limit

Andrew Cowan — Wed, 04 Apr 2007 01:59:43 GMT

You should really think very clearly before allocating a very large amount of swap since this can affect the performance of your machine, as the kernel has to continually scan and maintain these spaces.

A good strategy is to have even sized swap's on each disk, and try where possible to put them on the drives with the least IO. This not only improves performance, but can also increase system resilliance.

Re: Swap limit

Ivan Ferreira — Mon, 09 Apr 2007 10:58:26 GMT

The red hat official documentation for swap size limit is here:

http://www.redhat.com/magazine/017mar06/departments/tips_tricks/

Re: Swap limit

Stuart Browne — Tue, 10 Apr 2007 19:14:21 GMT

Hehe! I like the closing sentance of that magazine entry:

"Red Hat is working to update this information in the installation guide."

No wonder it's hard to get a straight answer out of their documentation :)

Re: Swap limit

Md.Shahabuddin — Thu, 18 Dec 2008 05:53:26 GMT

Thanks Folk !!!!!!!!!