8 General System Resource Management #

Depending on the server's range of applications and the hardware layout, the partitioning scheme can influence the machine's performance (although to a lesser extent only). It is beyond the scope of this manual to suggest different partitioning schemes for particular workloads. However, the following rules will positively affect performance. They do not apply when using an external storage system.

The installation scope has no direct influence on the machine's performance, but a carefully chosen scope of packages has advantages. It is recommended to install the minimum of packages needed to run the server. A system with a minimum set of packages is easier to maintain and has fewer potential security issues. Furthermore, a tailor made installation scope also ensures that no unnecessary services are started by default.

SUSE Linux Enterprise Server lets you customize the installation scope on the Installation Summary screen. By default, you can select or remove preconfigured patterns for specific tasks, but it is also possible to start the YaST Software Manager for a fine-grained package-based selection.

One or more of the following default patterns may not be needed in all cases:

A running X Window System consumes many resources and is rarely needed on a server. It is strongly recommended to start the system in target multi-user.target. You will still be able to remotely start graphical applications.

SUSE Linux Enterprise Server ships with several file systems, including Btrfs, Ext4, Ext3, Ext2, ReiserFS, and XFS. Each file system has its own advantages and disadvantages. Refer to Chapter 1, Overview of File Systems in Linux for detailed information.

Each file and directory in a file system has three time stamps associated with it: a time when the file was last read called access time, a time when the file data was last modified called modification time, and a time when the file metadata was last modified called change time. Keeping access time always up to date has significant performance overhead since every read-only access will incur a write operation. Thus by default every file system updates access time only if current file access time is older than a day or if it is older than file modification or change time. This feature is called relative access time and the corresponding mount option is relatime. Updates of access time can be completely disabled using the noatime mount option, however you need to verify your applications do not use it. This can be true for file and Web servers or for network storage. If the default relative access time update policy is not suitable for your applications, use the strictatime mount option.

Some file systems (for example Ext4) also support lazy time stamp updates. When this feature is enabled using the lazytime mount option, updates of all time stamps happen in memory but they are not written to disk. That happens only in response to fsync or sync system calls, when the file information is written due to another reason such as file size update, when time stamps are older than 24 hours, or when cached file information needs to be evicted from memory.

To update mount options used for a file system, either edit /etc/fstab directly, or use the Fstab Options dialog when editing or adding a partition with the YaST Partitioner.

The ionice command lets you prioritize disk access for single processes. This enables you to give less I/O priority to background processes with heavy disk access that are not time-critical, such as backup jobs. ionice also lets you raise the I/O priority for a specific process to make sure this process always has immediate access to the disk. The caveat with this feature is that standard writes are cached in the page cache and are written back to persistent storage only later by an independent kernel process. Thus, the I/O priority setting generally does not apply for these writes. Also be aware that the I/O class and priority settings are obeyed only by the CFQ I/O scheduler for the legacy block I/O path (refer to Section 12.2, “Available I/O Elevators”), and the BFQ I/O scheduler for the blk-mq I/O path (refer to Section 12.3, “Available I/O Elevators with blk-mq I/O path”). You can set the following three scheduling classes:

For more details and the exact command syntax refer to the ionice(1) man page. If you need more reliable control over bandwidth available to each application, use Kernel Control Groups as described in Section 9.2, “Setting Resource Limits”.