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Handbook:SPARC/Blocks/Disks
Partitions
Although it is theoretically possible to use the entire disk to house a Linux system, this is almost never done in practice. Instead, full disk block devices are split up in smaller, more manageable block devices. These are known as partitions or slices.
The first partition on the first SCSI disk is /dev/sda1, the second /dev/sda2 and so on.
The third partition on Sun systems is set aside as a special "whole disk" slice. This partition must not contain a file system.
Users who are used to the DOS partitioning scheme should note that Sun disklabels do not have "primary" and "extended" partitions. Instead, up to eight partitions are available per drive, with the third of these being reserved.
Designing a partition scheme
How many partitions and how big?
The number of partitions is highly dependent on the environment. For instance, if there are lots of users, then it is advised to have /home/ separate as it increases security and makes backups easier. If Gentoo is being installed to perform as a mail server, then /var/ should be separate as all mails are stored inside /var/. A good choice of filesystem will then maximize the performance. Game servers will have a separate /opt/ as most gaming servers are installed there. The reason is similar for the /home/ directory: security and backups. In most situations, /usr/ is to be kept big: not only will it contain the majority of applications, it typically also hosts the Gentoo ebuild repository (by default located at /usr/portage) which already takes around 650 MiB. This disk space estimate excludes the packages/ and distfiles/ directories that are generally stored within this ebuild repository.
It very much depends on what the administrator wants to achieve. Separate partitions or volumes have the following advantages:
- Choose the best performing filesystem for each partition or volume.
- The entire system cannot run out of free space if one defunct tool is continuously writing files to a partition or volume.
- If necessary, file system checks are reduced in time, as multiple checks can be done in parallel (although this advantage is more with multiple disks than it is with multiple partitions).
- Security can be enhanced by mounting some partitions or volumes read-only,
nosuid(setuid bits are ignored),noexec(executable bits are ignored) etc.
However, multiple partitions have disadvantages as well. If not configured properly, the system might have lots of free space on one partition and none on another. Another nuisance is that separate partitions - especially for important mount points like /usr/ or /var/ - often require the administrator to boot with an initramfs to mount the partition before other boot scripts start. This isn't always the case though, so results may vary.
There is also a 15-partition limit for SCSI and SATA unless the disk uses GPT labels.
What about swap space?
There is no perfect value for the swap partition. The purpose of swap space is to provide disk storage to the kernel when internal memory (RAM) is under pressure. A swap space allows for the kernel to move memory pages that are not likely to be accessed soon to disk (swap or page-out), freeing memory. Of course, if that memory is suddenly needed, these pages need to be put back in memory (page-in) which will take a while (as disks are very slow compared to internal memory).
When the system is not going to run memory intensive applications or the system has lots of memory available, then it probably does not need much swap space. However, swap space is also used to store the entire memory in case of hibernation. If the system is going to need hibernation, then a bigger swap space is necessary, often at least the amount of memory installed in the system.
Default partition scheme
The table below suggests a suitable starting point for most systems. Note that this is only an example, so feel free to use different partitioning schemes.
A separate /boot partition is generally not recommended on SPARC, as it complicates the bootloader configuration.
| Partition | Filesystem | Size | Mount Point | Description |
|---|---|---|---|---|
| /dev/sda1 | ext4 | <2 GB | / | Root partition. For SPARC64 systems with OBP versions 3 or less, this must be less than 2 GB in size, and the first partition on the disk. More recent OBP versions can deal with larger root partitions and, as such, can support having /usr, /var and other locations on the same partition. |
| /dev/sda2 | swap | 512 MB | none | Swap partition. For bootstrap and certain larger compiles, at least 512 MB of RAM (including swap) is required. |
| /dev/sda3 | none | Whole disk | none | Whole disk partition. This is required on SPARC systems. |
| /dev/sda4 | ext4 | at least 2 GB | /usr | /usr partition. Applications are installed here. By default this partition is also used for Portage data (which takes around 500 MB excluding source code). |
| /dev/sda5 | ext4 | at least 1 GB | /var | /var partition. Used for program-generated data. By default Portage uses this partition for temporary space whilst compiling. Certain larger applications such as Mozilla and LibreOffice.org can require over 1 GB of temporary space here when building. |
| /dev/sda6 | ext4 | remaining space | /home | /home partition. Used for users' home directories. |
Using fdisk to partition the disk
The following parts explain how to create the example partition layout described previously, namely:
| Partition | Description |
|---|---|
| /dev/sda1 | / |
| /dev/sda2 | swap |
| /dev/sda3 | whole disk slice |
| /dev/sda4 | /usr |
| /dev/sda5 | /var |
| /dev/sda6 | /home |
Change the partition layout as required. Remember to keep the root partition entirely within the first 2 GB of the disk for older systems. There is also a 15-partition limit for SCSI and SATA.
Firing up fdisk
Start fdisk with the disk as argument:
root #fdisk /dev/sdaCommand (m for help):
To view the available partitions, type in p:
Command (m for help):pDisk /dev/sda (Sun disk label): 64 heads, 32 sectors, 8635 cylinders Units = cylinders of 2048 * 512 bytes Device Flag Start End Blocks Id System /dev/sda1 0 488 499712 83 Linux native /dev/sda2 488 976 499712 82 Linux swap /dev/sda3 0 8635 8842240 5 Whole disk /dev/sda4 976 1953 1000448 83 Linux native /dev/sda5 1953 2144 195584 83 Linux native /dev/sda6 2144 8635 6646784 83 Linux native
Note the Sun disk label in the output. If this is missing, the disk is using the DOS-partitioning, not the Sun partitioning. In this case, use s to ensure that the disk has a Sun partition table:
Command (m for help):sBuilding a new sun disklabel. Changes will remain in memory only, until you decide to write them. After that, of course, the previous content won't be recoverable. Drive type ? auto configure 0 custom (with hardware detected defaults) a Quantum ProDrive 80S b Quantum ProDrive 105S c CDC Wren IV 94171-344 d IBM DPES-31080 e IBM DORS-32160 f IBM DNES-318350 g SEAGATE ST34371 h SUN0104 i SUN0207 j SUN0327 k SUN0340 l SUN0424 m SUN0535 n SUN0669 o SUN1.0G p SUN1.05 q SUN1.3G r SUN2.1G s IOMEGA Jaz Select type (? for auto, 0 for custom): 0 Heads (1-1024, default 64): Using default value 64 Sectors/track (1-1024, default 32): Using default value 32 Cylinders (1-65535, default 8635): Using default value 8635 Alternate cylinders (0-65535, default 2): Using default value 2 Physical cylinders (0-65535, default 8637): Using default value 8637 Rotation speed (rpm) (1-100000, default 5400): 10000 Interleave factor (1-32, default 1): Using default value 1 Extra sectors per cylinder (0-32, default 0): Using default value 0
The right values can be found in the documentation of the hard disk itself. The 'auto configure' option does not usually work.
Deleting existing partitions
It's time to delete any existing partitions. To do this, type d and hit Enter. Give the partition number to delete. To delete a pre-existing /dev/sda1, type:
Command (m for help):dPartition number (1-4): 1
Do not delete partition 3 (whole disk). This is required. If this partition does not exist, follow the "Creating a Sun Disklabel" instructions above.
After deleting all partitions except the Whole disk slice,a partition layout similar to the following should show up:
Command (m for help):pDisk /dev/sda (Sun disk label): 64 heads, 32 sectors, 8635 cylinders Units = cylinders of 2048 * 512 bytes Device Flag Start End Blocks Id System /dev/sda3 0 8635 8842240 5 Whole disk
Creating the root partition
Next create the root partition. To do this, type n to create a new partition, then type 1 to create the partition. When prompted for the first cylinder, hit Enter. When prompted for the last cylinder, type +512M to create a partition 512 MB in size. Make sure that the entire root partition fits within the first 2 GB of the disk. The output of these steps is as follows:
Command (m for help):nPartition number (1-8): 1 First cylinder (0-8635): (press Enter) Last cylinder or +size or +sizeM or +sizeK (0-8635, default 8635): +512M
When listing the partitions (through p), the following partition printout is shown:
Command (m for help):pDisk /dev/sda (Sun disk label): 64 heads, 32 sectors, 8635 cylinders Units = cylinders of 2048 * 512 bytes Device Flag Start End Blocks Id System /dev/sda1 0 488 499712 83 Linux native /dev/sda3 0 8635 8842240 5 Whole disk
Creating a swap partition
Next, let's create the swap partition. To do this, type n to create a new partition, then 2 to create the second partition, /dev/sda2 in our case. When prompted for the first cylinder, hit Enter. When prompted for the last cylinder, type +512M to create a partition 512 MB in size. After this, type t to set the partition type, 2 to select the partition just created and then type in 82 to set the partition type to "Linux Swap". After completing these steps, typing p should display a partition table that looks similar to this:
root #Command (m for help): root #pDisk /dev/sda (Sun disk label): 64 heads, 32 sectors, 8635 cylinders Units = cylinders of 2048 * 512 bytes Device Flag Start End Blocks Id System /dev/sda1 0 488 499712 83 Linux native /dev/sda2 488 976 499712 82 Linux swap /dev/sda3 0 8635 8842240 5 Whole disk
Creating the usr, var and home partitions
Finally, let's create the /usr, /var and /home partitions. As before, type n to create a new partition, then type 4 to create the third partition (we do not count the whole disk as being a partition), /dev/sda4 in our case. When prompted for the first cylinder, hit Enter. When prompted for the last cylinder, enter +2048M to create a partition 2 GB in size. Repeat this process for /dev/sda5 and sda6, using the desired sizes. When finished, the partition table will look similar to the following:
Command (m for help):pDisk /dev/sda (Sun disk label): 64 heads, 32 sectors, 8635 cylinders Units = cylinders of 2048 * 512 bytes Device Flag Start End Blocks Id System /dev/sda1 0 488 499712 83 Linux native /dev/sda2 488 976 499712 82 Linux swap /dev/sda3 0 8635 8842240 5 Whole disk /dev/sda4 976 1953 1000448 83 Linux native /dev/sda5 1953 2144 195584 83 Linux native /dev/sda6 2144 8635 6646784 83 Linux native
Save and exit
Save the partition layout and exit fdisk by typing w:
Command (m for help):w