Boot from SAN environments

Boot-from-SAN environments offer several advantages, including high performance, redundancy, and space consolidation. In these environments, the boot disk is on a remote SAN and not on the local host. The host communicates with the SAN through a host bus adapter (HBA). The HBA’s BIOS contains the instructions that enable the host to find the boot disk.

Boot from SAN depends on SAN-based disk arrays with either hardware Fibre Channel or HBA iSCSI adapter support on the host. For a fully redundant boot from SAN environment, you must configure multiple paths for I/O access. To do so, ensure that the root device has multipath support enabled. For information about whether multipath is available for your SAN environment, consult your storage vendor or administrator. If you have multiple paths available, you can enable multipathing in your XenServer deployment upon installation.

Warning:

Boot-from-SAN settings are not inherited during the upgrade process. When upgrading using the ISO or network-boot, follow the same instructions as used in the installation process below to ensure that multipath is correctly configured.

To install XenServer to a remote disk on a SAN with multipathing enabled:

  1. On the Welcome to XenServer screen, press F2.

  2. At the boot prompt, enter multipath

The XenServer installation process configures the XenServer host, which boots from a remote SAN with multipathing enabled.

To enable file system multipathing using PXE or UEFI installation, add device_mapper_multipath=yes to your configuration file. The following is an example configuration:

default xenserver
label xenserver
   kernel mboot.c32
   append /tftpboot/xenserver/xen.gz dom0_max_vcpus=1-2 \
   dom0_mem=1024M,max:1024M com1=115200,8n1 \
   console=com1,vga ---  /tftpboot/xenserver/vmlinuz \
   xencons=hvc console=hvc0 console=tty0 \
   device_mapper_multipath=yes \
   install ---  /tftpboot/xenserver/install.img

For additional information on storage multipathing in your XenServer environment, see Storage.

Software-boot-from-iSCSI for Cisco UCS

The Software-boot-from-iSCSI feature enables customers to install and boot XenServer from SAN using iSCSI. Using this feature, XenServer can be installed to, booted from, and run from a LUN provided by an iSCSI target. The iSCSI target is specified in the iSCSI Boot Firmware Table. This capability allows the root disk to be attached through iSCSI.

XenServer supports the following features for Software-boot-from-iSCSI:

  • Host installation through PXE-boot

  • Cisco UCS vNIC

    Software-boot-from-iSCSI has been tested in Legacy BIOS and UEFI boot mode by using Cisco UCS vNICs and Power Vault, NetApp, and EqualLogic arrays. Other configurations might work, however, they have not been validated.

  • Jumbo Frames (MTU=9000) configured with the Cisco UCS manager

  • Cisco UCS line-rate limiting

  • Untagged VLANs

  • Networks using the vSwitch back-end

  • LVHDoISCSI SRs and NFS SRs on the same or different SAN/NAS

  • Multipathing of the iSCSI root disk

  • Compatibility with common XenServer (Network, Maintenance) operations

Requirements

  • The primary management interface (IP addressable) and the network for VM traffic, must use separate interfaces.

  • Storage (iSCSI targets) must be on a separate Layer 3 (IP) network to all other network interfaces with IP addresses on the host.

  • Storage must be on the same subnet as the storage interface of the XenServer host.

Install XenServer by using CD media

Perform the following steps to install XenServer using a CD:

  1. Access the boot menu; at the boot: prompt enter menu.c32

  2. Use the cursor keys to select an installation option:

    • For a single path LUN, select install

    • For a multipathed LUN, select multipath

  3. Press the tab key.

    Edit the line ending with the following:

    ---  /install.img
    
  4. Using the cursor keys, edit this line to read:

    use_ibft ---  /install.img
    
  5. Press Enter.

    XenServer host installation proceeds as normal.

Install XenServer by using PXE

Perform the following steps to install XenServer using PXE:

Note:

Ensure that you add the keyword use_ibft in the kernel parameters. If multipathing is required, you must add device_mapper_multipath=enabled.

The following example shows PXE configuration for a single LUN:

label xenserver
kernel mboot.c32
append XS/xen.gz dom0_max_vcpus=2 dom0_mem=1024M,max:1024M
com1=115200,8n1 console=com1,vga ---  XS/vmlinuz xencons=hvc console=tty0
console=hvc0 use_ibft ---  XS/install.img

The following example shows PXE configuration for a multipathed LUN:

label xenserver
kernel mboot.c32
append XS/xen.gz dom0_max_vcpus=2 dom0_mem=1024M,max:1024M
com1=115200,8n1 console=com1,vga ---  XS/vmlinuz xencons=hvc console=tty0
console=hvc0 use_ibft device_mapper_multipath=enabled ---  XS/install.img

Boot from SAN environments