Installation prerequisites for the Db2 pureScale environment in a virtual machine (Intel Linux)

Before you install the IBM® Db2 pureScale environment, you must ensure that your system meets the following network, hardware, firmware, storage, and software requirements. You can use the db2prereqcheck command to check the software and firmware prerequisites of a specific Db2 version.

Supported virtual environments

You can install the Db2 pureScale environment on the following virtual machine (VM) configurations:

Table 1. Supported VM and operating systems
Hypervisor	Architecture	Minimum guest OS (Linux®)
VMware ESXi 6.0 or higher	x64 system that is supported by both the VM and Db2 pureScale	Any Linux distribution that is supported by both the VM and Db2 pureScale
VMware vSphere 6.0	x64 system that is supported by both the VM and Db2 pureScale	Any Linux distribution that is supported by both the VM and Db2 pureScale
Red Hat Enterprise Linux (RHEL) 7.5 and higher KVM	x64 system that is supported by both RHEL 7.5 and Db2 pureScale	RHEL 7.5 and higher

Note: If you use multiple physical servers in a VMware environment to host the VMs of a Db2 pureScale cluster, you can have only a single VM per physical server, per instance. This is due to each raw device mapping (RDM) disk can only be assigned to one virtual machine per physical server. See Note section under Table 2 below for detail.

Supported storage configurations

When installed on a virtual machine, the storage configurations of the Db2 pureScale environment are limited by the virtual environment.

Table 2. Supported VM storage configurations
Disk configuration	KVM hypervisor	VMware ESX/ESXi	Tiebreaker and I/O fencing
RDM disks in Physical Compatibility Mode¹	No	Yes	Yes
SAN disks in PCI pass-through mode²	Yes	No	Yes
Note: ¹Raw device mapping (RDM) disks are logical unit numbers (LUNs) that can be directly accessed from the VM guest operating system without going through a virtual machine file system (VMFS). RDM disk support is not available in KVM environments. To support tie-breaker disk and SCSI-3 PR I/O fencing, each RDM disk must be assigned to only one virtual machine per physical server. ²You can assign storage Fibre Channel (FC) adapters to the guest virtual machines by using the PCI device pass-through mode. After you assign storage adapters, you can directly access storage area network (SAN) disks from inside the guest VM. Tie-breaker disks and SCSI-3 PR I/O fencing are supported in this environment. Virtual disks are not supported

Network requirements

You must configure a network connection to install the Db2 pureScale environment.

It is also a requirement to keep the maximum transmission unit (MTU) size of the network interfaces at the default value of 1500. For more information on configuring the MTU size on Linux, see How do you change the MTU value on the Linux and Windows operating systems?

Table 3. Supported network configuration
Transport type	KVM	VMware ESX/ESXi
TCP/IP (sockets) ¹	Yes	Yes
RDMA over Ethernet (RoCE)	Yes²	Yes²
InfiniBand (IB)	No	No

Note:

¹If you are using a network card that is less than 10GE, you must set the DB2_SD_ALLOW_SLOW_NETWORK registry variable to ON.

²RDMA over Converged Ethernet (RoCE) is supported for KVM environment if the network adapter is assigned to the guest VM using the PCI device pass-through mode.

Additional installation requirements

If you are installing the Db2 pureScale environment on KVM, you must disable disk caching on virtual disks. Disk caching might cause data corruption if the same disk is used by multiple physical machines. If the disk is used by a single host, enabling disk write caching might result in missing data pages if the server is disconnected before the pages are updated on the physical disks. You can disable disk caching on KVM virtual disks by using the following command:

qemu-kvm -drive file=/dev/mapper/ImagesVolumeGroup 	Guest1,cache=none,if=virtio

For VMware ESX, there is no disk caching by the host.

Note: When you assign Fibre Channel adapters directly to the guest VMs using the PCI device pass- through mode, there is no disk caching.

The Db2 pureScale environment is based on the clustering of Db2 members. Therefore, you must configure all disks that are used by a Db2 pureScale cluster (via IBM Storage Scale) to allow concurrent read and write disk access between all VMs in the cluster.

For KVM virtual environments, you can enable concurrent disk access by specifying the “shareable” option when you configure virtual disks.
For VMware virtual environments, you can enable concurrent disk access by defining the multi-writer flag on the virtual disks. For more information, see the VMware documentation Disabling simultaneous write protection provided by VMFS using the multi-writer flag (http://kb.vmware.com/kb/1034165).