HP StorageWorks 9100 Extreme Data Storage System administration guide V1.0.2 (AN540-96018, February 2010)

For network services such as NFS and HTTP, clients use virtual hosts (so that the services are highly
available) instead of the server’s direct network interface. In addition, it is preferable to have all
servers involved equally in serving services, because this provides a scalable solution. This is done
by associating a different virtual host for each server and by organizing the environment so the client
population is split across each virtual host/server. A common way of doing this is to use DNS “round
robin,” where a DNS name is associated with multiple IP addresses (the virtual host IP addresses) and
DNS assigns a different IP address each time a lookup is performed on the name.
When specifying a virtual host, you specify a primary server and an ordered list of backup servers.
You also associate services (such as NFS, HTTP, or custom services) with the virtual host. Using
mxconsole or the mx(8) command you can construct arbitrarily complex layouts of virtual hosts,
services, and servers. However, exdsmgr provides commands to support NFS and HTTP services and
configures them to provide both scalability and high availability.
The virtual host layout for exdsmgr is as follows:
• The NFS and HTTP services are managed separately; that is, a given IP address might not be used
as a virtual host for both NFS and HTTP.
• Within each of the NFS and HTTP domains, exdsmgr manages a fixed set of servers. HP recom-
mends that you include all servers in the domain. However, it is possible to devote different sets
of servers to different functions. For example, servers one through three could be devoted to NFS
and servers four through eight to HTTP.
• For each domain, you must specify a virtual host IP address for each server. This means it is not
possible to only have three virtual host IP addresses spread over four servers.
• You can specify virtual hosts on the HP ExDS9100 system's external networks (for example, eth2
or eth3, and so on). However, for a given network, you must supply an IP address for all servers
in the domain as described above. It is possible not to use a network for a given domain. For
example, NFS could be served over eth2 and eth3, and HTTP served over eth4 and eth5 (that is,
eth2 not used by HTTP and eth4 not used by NFS).
• The exdsmgr always creates a “balanced” pattern for the primary and backup servers for a virtual
host. For example, the following table shows the priority order for a set of example virtual hosts
on four servers (“P” denotes the primary server):
glory7glory6glory5glory4
321P16.123.123.1
21P316.123.123.2
1P3216.123.123.3
P32116.123.123.4
As shown in the table, virtual host 16.123.123.2 has glory5 as its primary server, but fails over
to glory6, glory7, and then glory4 in that order.
• As a convenience, if you have a contiguous set of IP addresses available to you, you need only
specify the first IP address. However, if your IP address range is non-contiguous, you must specify
each address individually (as a comma-separated list of IP addresses).
When the NFS or HTTP domains are initially setup, the virtual hosts span the set of servers as ex-
plained above. When a new server is added to the system, the NFS and HTTP domains are not
affected; the new server will not serve NFS or HTTP services. You must use the exdsmgr modify
command with the addserver option as explained below to specify an additional IP address for
use by that server. The new server and associated vhost is added to the table in a way that
maintains the balanced set of vhosts.
HP ExDS9100 concepts28