A shared disk subsystem is required for each cluster in order to make data highly available. The Novell Cluster Services software must be installed in order to be able to mark devices as shareable, such as the devices you use for clustered pools and the device you use for the SBD (split-brain detector) during the cluster configuration.
Ensure that your shared storage devices meet the following requirements:
Novell Cluster Services supports the following shared disks:
Fibre Channel LUN (logical unit number) devices in a storage array
iSCSI LUN devices
SCSI disks (shared external drive arrays)
Before configuring Novell Cluster Services, the shared disk system must be properly set up and functional according to the manufacturer's instructions.
Prior to installation, verify that all the drives in your shared disk system are recognized by Linux by viewing a list of the devices on each server that you intend to add to your cluster. If any of the drives in the shared disk system do not show up in the list, consult the OES 2 documentation or the shared disk system documentation for troubleshooting information.
Devices where you plan to create shared file systems (such as NSS pools and Linux POSIX file systems) must be unpartitioned devices that can be managed by EVMS. NSS automatically partitions the device and lays down a Cluster Segment Manager on the partition when you use NSS tools to create a pool. You use the EVMS GUI to partition and create shared Linux POSIX file systems.
If this is a new cluster, the shared disk system must be connected to the first server so that the cluster partition can be created during the Novell Cluster Services install.
If your cluster uses physically shared storage resources, you must create an SBD (split-brain detector) partition for the cluster. You can create an SBD partition in YaST as part of the first node setup, or by using the SBD utility (sbdutil) later. Both the YaST new cluster setup and the SBD Utility support mirroring the SBD partition.
An SBD must be created before you attempt to create storage objects like pools or volumes for file system cluster resources, and before you configure a second node in the cluster. NSS management tools need the SBD to detect if a node is a member of the cluster and to get exclusive locks on physically shared storage.
For information about how SBD partitions work and how to create an SBD partition for an existing cluster, see Section 9.14, Creating or Deleting Cluster SBD Partitions.
Use the SAN storage array software to carve a LUN to use exclusively for the SBD partition. The device should have at least 20 MB of free available space. The minimum size is 8 MB. Connect the LUN device to all nodes in the cluster.
For device fault tolerance, you can mirror the SBD partition. Use the SAN storage array software to carve a second LUN of the same size to use as the mirror. Connect the LUN device to all nodes in the cluster.
The device you use to create the SBD partition must not be a software RAID device. A hardware RAID configured in a SAN array is seen as a regular device by the server.
NOTE:For an iSCSI SAN, a very small iSCSI device might rarely have uncommon CHS (cylinder-head-sector) geometry values. NSS prefers at least 32 sectors per track. If there are fewer than 32 sectors per track, NSS tools using EVMS can fail to create the partition or to mark the device as shareable. You can use fdisk to check for valid CHS values before you initialize and share the device. If necessary, you can use fdisk to set the sectors for the device (such as /dev/sdx) to 32:
fdisk -H 64 -S 32 /dev/sdx
Before you use YaST to set up the a cluster, you must initialize each SAN device that you created for the SBD, and mark each as Shareable for Clustering. When you mark the device as Shareable for Clustering, share information is added to the disk in a free-space partition that is about 4 MB in size. This space becomes part of the SBD partition.
IMPORTANT:The Novell Cluster Services software must already be installed in order to be able to mark the devices as shareable.
After you install Novell Cluster Services, but before you configure the cluster, you can initialize a device and set it to a shared state by using NSSMU, the Storage plug-in for Novell iManager, or an NSS utility called ncsinit.
When you configure a new cluster, you can specify how much free space to use for the SBD. You can specify theoption to use the entire device. If you specify a device to use as a mirror, the same amount of space is used. If the mirror device is bigger than the SBD device, you will not be able to use the excess free space on the mirror for other purposes.
Because an SBD partition ends on a cylinder boundary, the partition size might be slightly smaller than the size you specify.
You can also create the SBD by using the SBD Utility (sbdutil) before you configure a second node for the cluster and before you create file system cluster resources. The utility also supports mirroring the SBD partition. For information, see Section 9.14.3, Creating a Non-Mirrored Cluster SBD Partition.
If you are using iSCSI for shared disk system access, ensure that you have installed and configured the iSCSI initiators and targets (LUNs) and that they are working properly. The iSCSI target devices must be mounted on the server before the cluster resources are brought online.
We recommend that you use hardware RAID in the shared disk subsystem to add fault tolerance to the shared disk system.
Consider the following when using software RAIDs:
NSS software RAID is supported for shared disks.
Linux software RAID can be used in shared disk configurations that do not require the RAID to be concurrently active on multiple nodes. Linux software RAID cannot be used underneath clustered file systems (such as OCFS2, GFS, and CXFS) because Novell Cluster Services does not support concurrent activation.
WARNING:Activating Linux software RAID devices concurrently on multiple nodes can result in data corruption or inconsistencies.