2.1 Using the YaST Partitioner

With the expert partitioner, shown in Figure 2-1, manually modify the partitioning of one or several hard disks. Partitions can be added, deleted, resized, and edited. Also access the soft RAID and LVM configuration from this YaST module.

WARNING: Repartitioning the Running System

Although it is possible to repartition your system while it is running, the risk of making a mistake that causes data loss is very high. Try to avoid repartitioning your installed system and always do a complete backup of your data before attempting to do so.

Figure 2-1 The YaST Partitioner

All existing or suggested partitions on all connected hard disks are displayed in the list of the YaST Expert Partitioner dialog. Entire hard disks are listed as devices without numbers, such as /dev/sda. Partitions are listed as parts of these devices, such as /dev/sda1. The size, type, file system, and mount point of the hard disks and their partitions are also displayed. The mount point describes where the partition appears in the Linux file system tree.

If you run the expert dialog during installation, any free hard disk space is also listed and automatically selected. To provide more disk space to openSUSE®, free the needed space starting from the bottom toward the top of the list (starting from the last partition of a hard disk toward the first). For example, if you have three partitions, you cannot use the second exclusively for openSUSE and retain the third and first for other operating systems.

2.1.1 Partition Types

Every hard disk has a partition table with space for four entries. An entry in the partition table can correspond to a primary partition or an extended partition. Only one extended partition entry is allowed, however.

A primary partition simply consists of a continuous range of cylinders (physical disk areas) assigned to a particular operating system. With primary partitions only, you would be limited to four partitions per hard disk, because more do not fit in the partition table. This is why extended partitions are used. Extended partitions are also continuous ranges of disk cylinders, but an extended partition may itself be subdivided into logical partitions. Logical partitions do not require entries in the partition table. In other words, an extended partition is a container for logical partitions.

If you need more than four partitions, create an extended partition as the fourth partition or earlier. This extended partition should span the entire remaining free cylinder range. Then create multiple logical partitions within the extended partition. The maximum number of logical partitions is 15 on SCSI, SATA, and Firewire disks and 63 on (E)IDE disks. It does not matter which types of partitions are used for Linux. Primary and logical partitions both work fine.

2.1.2 Creating a Partition

To create a partition from scratch, proceed as follows:

Select Create. If several hard disks are connected, a selection dialog appears in which to select a hard disk for the new partition.
Specify the partition type (primary or extended). Create up to four primary partitions or up to three primary partitions and one extended partition. Within the extended partition, create several logical partitions (see Section 2.1.1, Partition Types).
Select the file system to use and a mount point. YaST suggests a mount point for each partition created. Refer to Section 16.0, File Systems in Linux for details on the various file systems.
Specify additional file system options if your setup requires them. This is necessary, for example, if you need persistent device names. For details on the available options, refer to Section 2.1.3, Editing a Partition.
Click OK > Apply to apply your partitioning setup and leave the partitioning module.

If you created the partition during installation, you are returned to the installation overview screen.

2.1.3 Editing a Partition

When you create a new partition or modify an existing partition, set various parameters. For new partitions, suitable parameters are set by YaST and usually do not require any modification. To edit your partition setup manually, proceed as follows:

Select the partition.
Click Edit to edit the partition and set the parameters:

File System ID

Even if you do not want to format the partition at this stage, assign it a file system ID to ensure that the partition is registered correctly. Possible values include Linux, Linux swap, Linux LVM, and Linux RAID. For LVM and RAID details, refer to Section 2.2, LVM Configuration and Section 2.3, Soft RAID Configuration.

File System

Change the file system or format the partition here. Changing the file system or reformatting partitions irreversibly deletes all data from the partition . For details on the various file systems, refer to Section 16.0, File Systems in Linux.

Swap is a special format that allows the partition to be used as virtual memory. Create a swap partition of at least 256 MB. However, if you use up your swap space, consider adding more memory to your system instead of adding more swap space.

Ext3 is the default file system for the Linux partitions. ReiserFS, JFS, and Ext3 are journaling file systems. These file systems are able to restore the system very quickly after a system crash, because write processes are logged during the operation. Furthermore, ReiserFS is very fast in handling lots of small files. Ext2 is not a journaling file system. However, it is rock solid and good for smaller partitions, because it does not require much disk space for management.

Encrypt File System

If you activate the encryption, all data is written to the hard disk in encrypted form. This increases the security of sensitive data, but slightly reduces the system speed, because the encryption takes some time. More information about the encryption of file systems is provided in Section 40.0, Encrypting Partitions and Files.

Fstab Options

Specify various parameters contained in the global file system administration file (/etc/fstab). The default settings should suffice for most setups. You can, for example, change the file system identification from the device name to a volume label. In the volume label, use all characters except / and space.

To get persistent devices names, use the mount option Device ID or UUID. In openSUSE, persistent device names are enabled by default.

If you intend to use quota on the file system, use the mount option Enable Quota Support. This must be done before you can define quotas for users in the YaST User Management module. For further information on how to configure user quota, refer to Section 5.2.4, Managing Quotas, (↑ Start-Up ).

Mount Point

Specify the directory at which the partition should be mounted in the file system tree. Select from various YaST proposals or enter any other name.
Select OK > Apply to activate the partition.

2.1.4 Expert Options

Expert opens a menu containing the following commands:

Reread Partition Table: Rereads the partitioning from disk. For example, you need this after manual partitioning in the text console.
Delete Partition Table and Disk Label: This completely overwrites the old partition table. For example, this can be helpful if you have problems with unconventional disk labels. Using this method, all data on the hard disk is lost.
Call iSCSI configuration: To access SCSI over IP block devices, you first have to configure iSCSI. This results in additionally available devices in the main partition list.

2.1.5 More Partitioning Tips

The following section comprises a few hints and tips on partitioning that should help you in taking the right decisions while setting up your system.

HINT: Cylinder Numbers

Note, that different partitioning tools may start counting the cylinders of a partition with 0 or with 1. When calculating the number of cylinders, you should always use the difference between the last and the first cylinder number and add one.

Foreign Partitions and fstab

If the partitioning is performed by YaST and other partitions are detected in the system, these partitions are also added to the /etc/fstab file to enable easy access to this data. This file contains all partitions in the system with their properties, such as the file system, mount point, and user permissions.

Example 2-1 /etc/fstab: Partition Data

/dev/disk/by-id/scsi-SATA_SAMSUNG_SV4002H0413J1FR917614-part1 /data1 auto noauto,user 0 0
/dev/disk/by-id/scsi-SATA_SAMSUNG_SV4002H0413J1FR917614-part5 /data2 auto noauto,user 0 0 
/dev/disk/by-id/scsi-SATA_SAMSUNG_SV4002H0413J1FR917614-part6 /data3 auto noauto,user 0 0

The partitions, regardless of whether they are Linux or FAT partitions, are specified with the options noauto and user. This allows any user to mount or unmount these partitions as needed. For security reasons, YaST does not automatically enter the exec option here, which is needed for executing programs from the location. However, to run programs from there, you can enter this option manually. This measure is necessary if you encounter system messages such as bad interpreter or Permission denied.

Using swap

Swap is used to extend the physically available memory. This way it is possible to use more memory than physical ram available. The memory management system of kernels before 2.4.10 needed swap as a safety measure. In those times, if you did not have twice the size of your ram in swap, the performance of the system suffered. This does not hold true anymore as these limitations no longer exist.

When the kernel runs out of memory, it swaps out pages of memory that are not used frequently. Therefore, the running applications have more memory available and even their caching works more smoothly.

If an application tries to allocate as much memory as it can possibly get, there are some problems with swap. There are three major cases to look at:

System with no swap: The application gets all memory that can be freed by any means. All caches are freed, and thus all other applications are slowed down. After several minutes, the out of memory killer mechanism of the kernel will become active and kill the process.
System with medіum sized swap (128 MB–256 MB): At first, the system is slowed down like a system without swap. After all physical ram has been used up, swap space is used as well. At this point, the system becomes very slow and it becomes impossible to run commands from remote. Depending on the speed of the hard disks that run the swap space, the system stays in this condition for about 10 to 15 minutes until the out of memory killer of the kernel resolves the issue.
System with lots of swap (several GB): You better do not have an application that is running wild and swapping frantically, in this case. If you do have this problem, the system will need many hours to recover. In the process, it is likely that other processes get timeouts and faults, leaving the system in an undefined state, even if the faulty process is killed. In this case, you better just reboot the machine hard and try to get it running again. Lots of swap is only useful if you have an application that relies on this feature. Such applications (like databases or graphics manipulation programs) have an option to directly use hard disk space for their needs. It is advisable to use this option instead of using lots of swap space.

If your system does not run wild, but needs more swap after some time, it is possible to extend the swap space online. If you prepared a partition for swap space, just add this partition with YaST. If you do not have a partition available, you may also just use a swap file to extend the swap. Swap files are generally slower than partitions, but compared to physical ram, both are extremely slow and the actual speed difference is not as important as one would think in the first place.

Adding a Swap File Manually

To add a swap file in the running system, proceed as follows:

Create an empty file in your system. For example, if you want to add a swap file with 128 MB swap at /var/lib/swap/swapfile, use the commands:
```
mkdir -p /var/lib/swap
dd if=/dev/zero of=/var/lib/swap/swapfile bs=1M count=128
```
Initialize this swap file with the command
```
mkswap /var/lib/swap/swapfile
```
Activate the swap with the command
```
swapon /var/lib/swap/swapfile
```
To disable this swap file, you use the command
```
swapoff /var/lib/swap/swapfile
```
Check the current available swap spaces with the command
```
cat /proc/swaps
```
Note, that at this point this is only temporary swap space. After the next reboot, it is not used anymore.
To enable this swap file permanently, add the following line to /etc/fstab:
```
/var/lib/swap/swapfile swap swap defaults 0 0
```

2.1.6 Partitioning and LVM

From the expert partitioner, access the LVM configuration with LVM (see Section 2.2, LVM Configuration). However, if a working LVM configuration already exists on your system, it is automatically activated as soon as you enter the LVM configuration for the first time in a session. In this case, any disks containing a partition belonging to an activated volume group cannot be repartitioned because the Linux kernel cannot reread the modified partition table of a hard disk when any partition on this disk is in use. However, if you already have a functioning LVM configuration on your system, physical repartitioning should not be necessary. Instead, change the configuration of the logical volumes.

At the beginning of the physical volumes (PVs), information about the volume is written to the partition. To reuse such a partition for other non-LVM purposes, it is advisable to delete the beginning of this volume. For example, in the VG system and PV /dev/sda2, do this with the command dd if=/dev/zero of=/dev/sda2 bs=512 count=1.

WARNING: File System for Booting

The file system used for booting (the root file system or /boot) must not be stored on an LVM logical volume. Instead, store it on a normal physical partition.