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Old 08-31-2009, 07:41 PM   #1
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Is it feasible to use an entire disk as swap space?

Has anyone configured a linux installation using an entire disk as swap space? I'm thinking about doing this with one or two 250G hard drives. We are experimenting with very large swap space.

I would think that would be feasible, and actually faster with more disks. But I've never tried it.
Old 08-31-2009, 08:03 PM   #2
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I doubt it - kswapd uses the block level device drivers. I think it checks the partition table as part of mkswap, but it's been a while since I looked at the code. A partition covering the whole disk would probably be o.k.
Multiple disks on separate controllers would be best - if the swap were all at the same priority; kswapd will stripe across them.
Old 09-01-2009, 07:23 AM   #3
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See here:

4.4.2. How large can my swap space be?

Currently, the maximum size of a swap partition is architecture-dependent. For i386, m68k, ARM and PowerPC, it is "officially" 2Gb. It is 128Gb on alpha, 1Gb on sparc, and 3Tb on sparc64. An opteron on the 2.6 kernel can write to a 16 Tb swap partition. For linux kernels 2.1 and earlier, the limit is 128Mb. The partition may be larger than 128 MB, but excess space is never used. If you want more than 128 MB of swap for a 2.1 and earlier kernel, you have to create multiple swap partitions (8 max). After 2.4, 32 swap areas are "officially" possible. See setting up swap for details.

footnote: "official" max swap size: With kernel 2.4, the limit is 64 swap spaces at a maximum of 64Gb each, although this is not reflected in the man page for mkswap. With the 64 bit opteron on the 2.6 kernel, 128 swap areas are permitted, each a whopping 16 Tb! (thanks to Peter Chubb for the calculation)
It depends a lot on your system ... kernel version, architecture, etc.

I very much doubt you could improve performance in this way, at least not significantly.


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