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What Partitions do I need?

Boot Drive:
If you want to boot your operating system from the drive you are about to partition, you will need:

Any other drive:

Discussion:

Boot Partition:
Your boot partition ought to be a primary partition, not a logical partition. This will ease recovery in case of disaster, but it is not technically necessary. It must be of type 0x83 "Linux native". If you are using lilo, your boot partition must be contained within the first 1024 cylinders of the drive. (Typically, the boot partition need only contain the kernel image.)
If you have more than one boot partition (from other OSs, for example,) keep them all in the first 1024 cylinders (All DOS partitions must be within the first 1024). If you are using a means other than lilo loading your kernel (for example, a boot disk or the LOADLIN.EXE MS-DOS based Linux loader), the partition can be anywhere. See the Large-disk HOWTO for details.

Swap Partition:

Unless you swap to files you will need a dedicated swap partition. It must be of type 0x82 "Linux swap".  It may be positioned anywhere on the disk (but see notes on placement). Either a primary or logical partition can be used for swap. More than one swap partition can exist on a drive. 8 total (across drives) are permitted. See notes on swap size.

Logical Partition:

A single primary partition must be used as a container (extended partition) for the logical partitions. The extended partition can go anywhere on the disk. The logical partitions must be contiguous, but needn't fill the extended partition.


File Systems

Which file systems need their own partitions?

Everything in your linux file system can go in the same (single) partition. However, there are circumstances when you may want to restrict the growth of certain file systems. For example, if your mail spool was in the same partition as your root fs and it filled the remaining space in the partition, your computer would basically hang.

/var This fs contains spool directories such as those for mail and printing. In addition, it contains the error log directory. If your machine is a server and develops a chronic error, those msgs can fill the partition. Server computers ought to have /var in a different partition than /.
/usr This is where most executable binaries go. In addition, the kernel source tree goes here, and much documentation.
/tmp Some programs write temporary data files here. Usually, they are quite small. However, if you run computationally intensive jobs, like science or engineering applications, hundreds of megabytes could be required for brief periods of time. In this case, keep /tmp in a different partition than /.
/home This is where users home directories go. If you do not impose quotas on your users, this ought to be in its own partition.
/boot This is where your kernel images go. If you use MSDOS, which must go in the first 1024 cylinders, you need to at least get this partition in there in order to ensure that lilo can see it. If you have a drive larger than 1024 cylinders, making this your first partition guarantees that it will be visible to lilo.

File lifetimes and backup cycles as partitioning criteria

With ext2, partitioning decisions should be governed by backup considerations and to avoid external fragmentation from different file lifetimes.

Files have lifetimes. After a file has been created, it will remain some time on the system and then be removed. File lifetime varies greatly throughout the system and is partly dependent on the pathname of the file. For example, files in /bin, /sbin, /usr/sbin, /usr/bin and similar directories are likely to have a very long lifetime: many months and above. Files in /home are likely to have a medium lifetime: several weeks or so. File in /var are usually short lived: Almost no file in /var/spool/news will remain longer than a few days, files in /var/spool/lpd measure their lifetime in minutes or less.

For backup it is useful if the amount of daily backup is smaller than the capacity of a single backup medium. A daily backup can be a complete backup or an incremental backup.

You can decide to keep your partition sizes small enough that they fit completely onto one backup medium (choose daily full backups). In any case a partition should be small enough that its daily delta (all modified files) fits onto one backup medium (choose incremental backup and expect to change backup media for the weekly/monthly full dump - no unattended operation possible).

Your backup strategy depends on that decision.

When planning and buying disk space, remember to set aside a sufficient amount of money for backup! Unbackuped data is worthless! Data reproduction costs are much higher than backup costs for virtually everyone!

For performance it is useful to keep files of different lifetimes on different partitions. This way the short lived files on the news partition may be fragmented very heavily. This has no impact on the performance of the / or /home partition.


Swap Partitions

How large should my swap space be?

If you have decided to use a dedicated swap partition, which is generally a Good Idea [tm], follow these guidelines for estimating its size:


A very old rule of thumb in the days of the PDP and the Vax was that the size of the working set of a program is about 25% of its virtual size. Thus it is probably useless to provide more swap than three times your RAM.

But keep in mind that this is just a rule of thumb. It is easily possible to create scenarios where programs have extremely large or extremely small working sets. For example, a simulation program with a large data set that is accessed in a very random fashion would have almost no noticeable locality of reference in its data segment, so its working set would be quite large.

On the other hand, an xv with many simultaneously opened JPEGs, all but one iconified, would have a very large data segment. But image transformations are all done on one single image, most of the memory occupied by xv is never touched. The same is true for an editor with many editor windows where only one window is being modified at a time. These programs have - if they are designed properly - a very high locality of reference and large parts of them can be kept swapped out without too severe performance impact.

One could suspect that the 25% number from the age of the command line is no longer true for modern GUI programs editing multiple documents, but I know of no newer papers that try to verify these numbers.

So for a configuration with 16 MB RAM, no swap is needed for a minimal configuration and more than 48 MB of swap are probably useless. The exact amount of memory needed depends on the application mix on the machine (what did you expect?).

Where should I put my swap space?

Summary: Put your swap on a fast disk with many heads that is not busy doing other things. If you have multiple disks: Split swap and scatter it over all your disks or even different controllers.

Even better: Buy more RAM.


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