Chapter 4. Managing EVMS Devices

This section describes how to initialize a disk for EVMS management by adding a segment management container to manage the partitions that you later add to the disk.

4.1. Understanding Disk Segmentation

In EVMS, you initialize a disk by assigning a segment manager to it. The segment manager creates metadata for the disk and exposes its free space so you can subdivide it into one or multiple segments (also called partitions).

4.1.1. Segment Managers

The most commonly used segment manager is the DOS Segment Manager. The following table describes the segment managers available in EVMS.

Table 4.1. EVMS Segment Managers

Segment Manager

Description

DOS

The standard MS-DOS disk partitioning scheme. It is the most commonly used partitioning scheme for Linux, NetWare, Windows, OS/2, BSD, Solaris X86, and UnixWare.

GPT (Globally Unique Identifier (GUID) Partitioning Table)

A partitioning scheme used for IA-64 platforms, as defined in the Intel Extensible Firmware Interface (EIF) Specification. It is not compatible with DOS, Windows, or OS/2 systems.

The GUID is also known as Universally Unique Identifier (UUID). The GPT combines time and space descriptors to create this unique 128-bit tag for the disk and its segments.

S/390

A partitioning scheme used exclusively for System/390 mainframes.

Cluster

A partitioning scheme for high-availability clusters. It provides a GUID for the disk, creates an EVMS container for the shared cluster devices, and specifies a node ID for the node that owns the device and the cluster ID.

BSD

A partitioning scheme for BSD UNIX.

MAC

A partitioning scheme for Mac-OS partitions.


4.1.2. Disk Segments

After you initialize the disk by adding a segment manager, you see metadata and free space segments on the disk. You can then create one or multiple data segments in a disk segment.

Table 4.2. Disk Segment Types

Segment Type

Description

Metadata

A set of contiguous sectors that contain information needed by the segment manager.

Free Space

A set of contiguous sectors that are unallocated or not in use. Free space can be used to create a segment.

Data

A set of contiguous sectors that has been allocated from a disk. The segment might be in use for a volume or a software RAID.


4.2. Initializing Disks

You must initialize new disks and disks that you want to reformat. After the disk is initialized, you can subdivide, or carve, the device into one or more disk segments for your file systems.

4.2.1. Before You Begin

If you use large disks or disk arrays, use the vendor’s tools to carve them into the sizes that are usable for the management tools you plan to use. For example, the md driver recognizes disks only up to 2 TB in size, so the limit also applies to the md plug-in for EVMS. Software RAID devices you create with EVMS can be larger than 2 TB, of course, because the md driver plug-in manages the disks underneath that storage structure.

When you boot the server, EVMS scans and recognizes all devices it manages. If you add a new device to the server or create a device using mkfs, EVMS automatically mounts it on reboot under /dev/evms as a compatibility volume, such as /dev/evms/sdb.

[Important]

If you cannot find a new disk, device, or volume, look under /dev/evms in a file browser, or look for compatibility volumes in the Volumes Manager in the EVMS GUI (evmsgui).

4.2.2. Guidelines

Consider the following guidelines when initializing a disk:

  • EVMS might allow you to create segments without first adding a segment manager for the disk, but it is best to explicitly add a segment manager to avoid problems later.

    [Important]

    You must add a Cluster segment manager if you plan to use the devices for volumes that you want to share as cluster resources.

  • When you initialize an existing disk that is already formatted, the process of adding a segment manager destroys all data on the disk. If you want to keep the data on the disk, make sure to back up the data before you begin this process.

  • For existing disks on the system or disks that you move from another system, you must delete any existing volume management structures, and remove any segment managers. This removes the device’s metadata and data, and destroys all data on the disk.

    [Warning]

    Do not initialize the device that contains your current system disk or any device that contains the /boot, swap, or root (/) volumes.

  • If a new disk does not show up in the list of Available Objects, look for it in the Volumes list to see if the disk shows up as a compatibility volume. For example, a new disk sdb would show up as /dev/evms/sdb. Delete it from the Volumes list to force the disk to show up in Available Objects, then create segments as desired.

4.2.3. Adding a Segment Manager

Use the following procedure to assign a segment manager to device for servers using x86, x64, and IA64 controllers. This option is not available for S390 platforms, so simply continue with configuring software RAIDs or file system partitions, as desired.

[Warning]

Adding a segment manager initializes the disk, completely removing all the segments it contains. All the data stored on the device is lost.

  1. If the disk has any existing volume management structures or an existing segment manager, remove them.

    1. Select Actions+Delete+Volume to view the Volumes list.

    2. Select any existing volume management structures on the device, then click Delete.

    3. Select Actions+Remove+Segment Manager from Storage Object.

    4. Select the type of Segment Manager in use, then click Next.

    5. Select the device, then click Remove.

  2. If the disk is a new one that is listed as a compatibility volume in the Volumes list, delete it as a compatibility volume.

    1. Select Actions+Delete+Volume to view the Volumes list.

    2. Select the device, then click Delete.

  3. Add the Segment Manager.

    1. In the list of Availability Objects, select the device, then click Actions+Add+Segment Manager to Storage Object.

    2. From the list, select one of the following types of segment manager, then click Next.

      • DOS Segment Manager (the most common choice)

      • GPT Segment Manager (for IA-64 platforms)

      • Cluster Segment Manager (available only if it is a viable option for the selected disk)

    3. Select the device from the list of Plugin Acceptable Objects, then click Next.

    4. If required, specify the disk type as Linux.

    5. Click Add to create the segment management container for the disk, then click OK to dismiss the confirmation message.

4.3. Removing the Segment Manager from a Device

  1. If the disk has any existing volume management structures, remove them.

    1. Select Actions+Delete+Volume to view the Volumes list.

    2. Select any existing volume management structures on the device, then click Delete.

  2. Select Actions+Remove+Segment Manager from Storage Object.

  3. Select the type of Segment Manager in use, then click Next.

  4. Select the device, then click Remove.

4.4. Creating Disk Segments (or Partitions)

  1. In EVMS, select Actions+Create+Segment to see a list of segment managers.

  2. From the list, select the segment manager for the device you want to manage, then click Next.

    • DOS Segment Manager (the most common choice)

    • GPT Segment Manager (for IA-64 platforms)

    • Cluster Segment Manager (available only if it is a viable option for the selected disk)

    For information about these and other segment managers available, see Section 4.1.1, “Segment Managers”.

  3. Select the storage object that you want to segment, then click Next.

  4. Complete the required configuration options for the segment, and modify default values as desired.

    • Size (MB): Specify the amount of space (in MB) that you want to use. Use the arrows or type a value. The interface corrects the value to the lower or upper size limit if you specify a size that is too small or that exceeds the amount of free space available.

    • Offset (Sectors): Specify the number of sectors to skip before beginning this partition if you want to leave free space in front of it.

    • Partition Type: From the drop-down list, select Linux (default), Linux Swap, Linux LVM, NTFS, HPFS, FAT16, or Other Partition Type.

    • Partition Type ID: This value changes automatically based on the Partition Type value, except for the Other Partition Type option, where you must manually enter a value.

    • Bootable: Click Yes to make a primary partition active so that you can boot from it, or click No to make it unbootable. No is the only option if you are creating a logical partition.

    • Primary Partition: Click Yes for a primary partition, or click No for a logical partition.

    Required settings are denoted in the page by an asterisk (*). All required fields must be completed to make the Create button active.

  5. Click Create to create the segment.

  6. Verify that the new segment appears in the Segment list.

4.5. Configuring Mount Options for Devices

The following table describes the Fstab Options that are configurable in YaST. The values are written to the /etc/fstab file and are applied upon reboot.

Table 4.3. Fstab Options in YaST

Fstab Option

Description

Mount by

Volume label

A useful name to help you easily identify the volume on the server. By default, this field is empty.

Mount read-only

Select the check box to enable this option. It is deselected (disabled) by default.

If this option is enabled, files and directories cannot be modified or saved on the volume.

No access time

Select the check box to enable this option. It is deselected (disabled) by default.

By default, the Linux open(2) command updates the access time whenever a file is opened. The No Access Time option disables the updating of access time, so that reading a file does not update its access time. Enabling the No Access Time option allows you to back up a volume without modifying the access times of its files.

Mountable by user

Select the check box to enable this option. It is deselected (disabled) by default.

If this option is enabled, the volume can be mounted by any user; root privileges are not required.

Do Not Mount at System Start-up

Select the check box to enable this option. It is deselected (disabled) by default.

The system volumes such as /boot, swap, and root (/) should all be mounted at system start. For other volumes, enable this option for a volume if you want to mount it manually later using the mount command at a terminal console prompt.

Data journaling mode

For journaling file systems, select the preferred journaling mode:

  • Ordered: Writes data to the file system, then enters the metadata in the journal. This is the default.

  • Journal: Writes data twice; once to the journal, then to the file system.

  • Writeback: Writes data to the file system and writes metadata in the journal, but the writes are performed in any order.

Access Control LIsts (ACL)

Select this option to enable access control lists on the file system. It is enabled by default.

Extended user attributes

Select this option to enable extended user attributes on the file system. It is enabled by default.

Arbitrary option value

Specify any mount option that is legal for the Mount Options column for a device entry in the /etc/fstab file. Use a comma with no spaces to separate multiple options.


You can modify these values for each entry by editing the /etc/fstab file, or use the following procedure to modify the mount options for a volume in the /etc/fstab file from YaST.

  1. Open YaST, then click System+Partitioning.

  2. Select the device you want to modify, then click Fstab Options.

    Fstab Options Dialog Box
  3. Modify the settings as desired, then click OK to accept your changes.

4.6. What’s Next

If multiple paths exist between your host bus adapters (HBAs) and the storage devices, configure multipathing for the devices before creating software RAIDs or file system volumes on the devices. For information, see Chapter 5, Managing Multipath I/O for Devices.

If you want to configure software RAIDs, do it before you create file systems on the devices. For information, see Chapter 6, Managing Software RAIDs with EVMS.


SUSE® Linux Enterprise Server Storage Administration Guide 10 SP3/SP4