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Where do I put my swap? Debian installation gives 2 choices: (1) at the end or (2) at the beginning of the disk space. What is optimal?

What is the optimal amount of swap given my computer has 512Mb RAM? Should I have more than one swap?

Should I define swap space as a logical or primary partition?

I'm installing Debian 6 testing 32bit on a 40Gb disk.

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Note that the optimal swap size depends on the use of your machine. You won't define the same size for a desktop, a server or an embedded system. –  rahmu Sep 8 '11 at 8:32
    
Mine is a desktop if that helps. –  ptrcao Sep 8 '11 at 8:41
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3 Answers

A hard disk is usually faster at the start than at the end. But I'm not sure if it makes a significant difference.

Optimal amount of swap depends on how many programs you run and how excessively swap is used. 1G won't hurt, though. More than one swap is not necessary.

You can put your swap

  • in a primary partition,
  • in a logical partition,
  • on a LVM volume (that's what I do)
  • and even in a file - that is said to make no noticeable difference nowadays.

You even can do a combined way: use a 512M..1G swap partition permanenty and add a swap file if you need.

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Do not forget that you need around 1Mb of real memory permanently allocated by kernel for each 1Gb of virtual memory available. –  andcoz Sep 8 '11 at 9:00
    
@glglgl: Why is it faster at the start? –  ptrcao Sep 8 '11 at 11:02
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The revolution rate is constant, but there are more data at the border of the HDD (start) than in the center (end) as the area is bigger there. See also partition.radified.com/partitioning_2.htm. –  glglgl Sep 8 '11 at 11:07
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Where do I put my swap?

I don't expect that it matters much (performance). Just go with the default.

What is the optimal amount of swap given my computer has 512Mb RAM?

I've seen some place mentioned that you should have roughly twice the amount of swap as the amount of RAM.

Should I have more than one swap?

Why would you do that? I don't even know if Linux can use more than one swap area (haven't checked).

Should I define swap space as a logical or primary partition?

Rather leave it as logical, just so you don't run out of partitions if you create more.

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I've done some reading and there's a lot of talk about the travel time of the head. You mean none of these considerations make a difference? –  ptrcao Sep 8 '11 at 8:07
    
Not enough to bother caring about. –  Tshepang Sep 8 '11 at 8:25
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From man mkswap: Presently, Linux allows 32 swap areas (this was 8 before Linux 2.4.10). –  andcoz Sep 8 '11 at 8:49
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Most disks use zoned recording, where a more or less constant physical density of data is maintained over the disk. This means that tracks closer to the edge of the disk will have more sectors. Data reads from these regions will be a bit faster than data reads from tracks close to the hub.

On modern disks, the tracks closest to the edge start at 0, with higher numbers being closer to the centre of the disk. Therefore partitions on lower numbered tracks towards will perform slightly faster. As an aside, the actual heads x sectors x tracks layout on the drive is virtualised - the values you see are translated to the physical geometry behind the scenes by the drive's firmware and have nothing to do with the actual layout of the drive.

A rule of thumb for swap space is to have about twice as much as your physical RAM. A 1GB swap partition sounds reasonable.

For swap, making it a primary or logical partition is irrelevant, although there are a couple of caveats that may bite you on really old machines.

On older systems, some BIOSs couldn't boot from a partition that started outside track 1024. The /boot area could be either left under / or mounted as a separate /boot partition. In either case the entire partition where /boot resides would need to be within track 1024 and may have needed to be a primary partition. This issue normally does not affect swap partitions.

Note that most PCs built from the mid-late 1990s onwards will not have this issue, so it probably does not affect you.

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