The other factor to consider when scoping fan-in ratios is the maximum number of
concurrent iSCSI sessions per gateway port
that the storage vendor has certified. An iSCSI
gateway might support up to 50 iSCSI sessions
per Gigabit Ethernet port, whereas the storage
vendor might certify only a more conservative
20 sessions per port. Each storage vendor does
its own certification and testing of iSCSI gateway products and sets its own supported limit
for each.
Bringing iSCSI Servers into
the SAN
As you plan for integrating iSCSI-attached
Windows servers into your SAN, identify the collective storage capacity required for all the
newly attached iSCSI servers, the average storage traffic generated by the second-tier applications running on the servers, and the initial
fan-in ratio that best suits the aggregate traffic
load to help size both SAN and iSCSI gateway
requirements. It might be fairly easy to identify
the amount of storage capacity each second-tier server needs, but it's usually more difficult
to identify storage traffic patterns and loads,
particularly for "bursty" applications. It's best,
then, to start with a fairly conservative fan-in
ratio (e.g., 7:1 or lower) and gradually increase
the number of iSCSI servers per iSCSI gateway
port until you reach the optimum fan-in for
your situation.
Deploying second-tier iSCSI servers into
an existing Fibre Channel SAN requires three
basic steps: configuring the existing Fibre
Channel storage array for additional hosts,
setting up the iSCSI gateway for both virtual
Fibre Channel initiator and virtual iSCSI target connections, and installing the Microsoft
iSCSI initiator and iSNS (if desired) software
for host connection. No one step is particularly
difficult, but the process might require collaboration between server administrators and
SAN administrators if those functions aren't
combined in your environment.
Step 1: Configuring SAN storage for new iSCSI hosts. Because you're using an iSCSI
gateway to integrate additional servers, no special process is required to configure additional
storage capacity. From the SAN administrator's
standpoint, the new LUNs are being configured for traditional Fibre Channel initiators,
which in fact have a virtual existence within
the iSCSI gateway. Consequently, you create
additional LUNs with the desired capacity as
usual by using the storage vendor's configuration utility, and the appropriate number of new
storage ports (determined by the fan-in ratio)
are connected to the SAN fabric.
Although an iSCSI gateway platform might
allow direct connection between the gateway
and SAN storage, data center administrators
might prefer to drive all storage connections
through Fibre Channel directors or switches.
In this case, you connect both storage ports
and iSCSI gateway Fibre Channel ports to the
fabric and configure zoning or LUN masking
at the fabric level. Each new storage port is
represented by a unique World Wide Name
(WWN), which you use to configure zoning
and connectivity to the iSCSI gateway.
Every storage vendor provides its own
management utility for creating LUNs from the
total capacity of the storage array. Typically,
these utilities are GUI-based and fairly simple
to configure. Likewise, individual fabric switch
vendors provide utilities for configuring switch
ports, zone groups, and LUN masking. It's
important to remember that although you're
configuring SAN resources to connect iSCSI
initiators, the storage arrays and fabric see only
Fibre Channel initiators proxied by the iSCSI
gateway.
Step 2: Setting up the iSCSI gateway. The
iSCSI gateway configuration has two basic
components. You configure and bind the
iSCSI initiators to their respective virtual iSCSI
targets. And, likewise, you configure and bind
the real Fibre Channel targets to their respective virtual Fibre Channel initiators. Typically,
the configuration utility provided by the iSCSI
gateway vendor streamlines this dual process
so that when you configure an iSCSI initiator,
the proxy Fibre Channel initiator is created
automatically.
You register iSCSI initiators by iSCSI identifiers and register SAN resources by WWNs
and Fibre Channel IDs (FCIDs) on the iSCSI
gateway. You must determine these respective
identifiers in advance to properly configure the
iSCSI gateway. In Figure 3, the configuration
utility for an iSCSI gateway (in this example,
a Brocade M2640) shows an iSCSI initiator
defined by iSCSI identifier and alias, IP address,
and proxied WWNs.
The iSCSI gateway might include additional utilities for implementing CHAP or
IPsec for security. As with general address
information, you should determine any CHAP
parameters or IPsec addressing in advance to
simplify gateway installation.
Because each iSCSI gateway vendor provides its own unique utility for configuring
iSCSI hosts and SAN targets, I can't provide a
step-by-step example for gateway configuration. The common requirements, though, are
to configure iSCSI initiator properties, configure proxied targets, and define LUN masking
parameters for the target volumes.
Step 3: Configure the iSCSI hosts. Along
with its free iSCSI Software Initiator, Microsoft
provides detailed installation instructions in
a downloadable users' guide. Once you've
installed the software on a Windows server, the
basic steps are to assign an iSCSI initiator node
name for the server, configure any desired
security features, discover (via iSNS) or define
targets available for the server, and bind the
iSCSI host to the appropriate targets.
After you've set the initiator parameters on
the General tab of the iSCSI Initiator Properties dialog box, use the Discovery tab to either discover through iSNS or manually enter the IP
address of intended targets. If you install iSNS
on a LAN-attached server, it will periodically
check for the existence of any additional iSCSI
targets. In this example, those targets are represented by the iSCSI gateway. Alternatively,
click Add in the Target Portals area of the Discovery tab to manually identify targets.
Register
