ISCSI SANs are quickly gaining acceptance in small business and
enterprise environments, spurred on by the simplicity, low cost,
and ubiquitous availability of Ethernet networks. Still, the
benefits of
iSCSI are often tempered by performance limitations when iSCSI
storage traffic is added on top of everyday user LAN traffic. In
many cases, the impact of iSCSI traffic is mitigated by limiting it
to its own network segment or VLAN. One means of improving iSCSI
traffic performance is to include TOE (TCI/IP Offload Engine)
capability on the Ethernet card itself. An iSCSI TOE allows the
network adapter to process iSCSI traffic (often all Ethernet LAN
traffic) locally -- relieving those burdensome processing tasks
from the host server or other computers connected to the LAN. To
implement this capability, iSCSI servers must be upgraded with
Ethernet NICs that include a TOE chip onboard.
Although the selection of iSCSI TOE cards is generally limited
to just a few manufacturers, it's important to consider the
available ports, host interface, and other card characteristics
before making a purchase. In addition, the TOE card should fully
support the traffic types handled on each server. Now that you've
reviewed the
essential issues involved in any SAN upgrade, this chapter
covers the specific considerations involved in iSCSI TOE cards.
Following the considerations, you'll find a series of
specifications to help make on-the-spot product comparisons between
vendors, including Alacritech, LeWiz Communications Inc., and
QLogic Corp.
Evaluate the price versus the additional performance. The
main premise behind TOE cards is that their onboard TCP/IP
instruction stack processing capability helps to unburden the
server's main processor(s). However, for this to make any kind of
performance difference, the server's CPU should be at or near its
maximum capacity. That is, if the CPU isn't being stressed, the
addition of a TOE won't make much of a difference in the server's
performance -- effectively wasting the additional money spent on
the cards. Lab testing can help to identify the true performance
impact of a TOE card.
Consider the traffic types supported. Some iSCSI TOE
cards focus their acceleration specifically on iSCSI commands, and
may not accelerate other types of TCP/IP traffic. This may be fine
if you're configuring servers specifically for an iSCSI network
segment. However, most iSCSI TOE cards will accelerate all types of
TCP traffic including email data, Web data, file serving, and
backup in addition to iSCSI storage tasks.
Consider the compatibility with your environment. Experts
recommend a close review of operating system and server
compatibility followed by application support, For example, if the
iSCSI TOE card is intended for a Microsoft Windows system, check
the level of integration and support for Microsoft Scalable
Networking Pack (SNP) first available for Windows Server 2003 in
late 2006. Also check to see if the TOE card can be configured as
an initiator, target, or both -- especially if the TOE card is
slated for a storage appliance or server. In many cases, iSCSI
vendors will qualify network adapters, switches, servers, and
appliances, so always reference the vendor's product compatibility
matrix for product suggestions and known caveats.
Consider the host
interconnects. The vast majority of iSCSI TOE cards are
compatible with PCI-X or PCIe (PCI Express) slots on the host
server. Most iSCSI TOE card manufacturers offer both PCI-X and PCIe
variants, so it's important to first identify the slot type and
purchase the corresponding card model. For example, the QLogic
QLA4050C/QLA4052C iSCSI TOE cards are built for PCI-X, while the
Alacritech SEN2100 Accelerator card is made for PCIe.
Plan enough ports for special features. iSCSI TOE cards
typically offer one, two, or four Gigabit Ethernet (GigE) ports.
Cards can be selected with copper or optical fiber connectivity.
Additional cards would then be needed to supply additional ports.
When considering an iSCSI TOE card purchase or upgrade, be sure to
purchase enough ports to support iSCSI SAN features on each server
such as failover or high availability. Remember that features may
demand additional software components. For example, path manager
software may be needed for load balancing and failover capability.
Additional software can add to the software maintenance overhead
for each iSCSI system.
Consider the need for bootability. Many Fibre Channel
HBAs include the ability to boot servers from the storage network
rather than relying on local storage. An increasing number of iSCSI
TOE cards offer the same boot capability so that servers can boot
from an iSCSI storage system or appliance. For example, Alacritech
iSCSI TOE cards support booting through PXE with their emBoot
software.
Evaluate the management tools. Many iSCSI TOE cards
employ software tools for configuration and management. Consider
the versatility and interoperability of the management tools. Tools
that recognize and handle cards from various vendors anywhere
across the iSCSI fabric can be far more useful than specialized
utilities that only work with a specific vendor's HBAs. For
example, the QLogic SANBlade (QLA4050C/QLA4052C) iSCSI card uses
their SANsurfer device manager utility and CLI, while Alacritech's
iSCSI cards rely on management tools already integrated into
Windows as part of the Scalable Networking Pack (SNP).
The iSCSI TOE card specifications page in this chapter covers
the following products:
- Alacritech; SEN2000 Accelerator card
- Alacritech; SEN2100 Accelerator card
- Alacritech; SES2000 Accelerator card
- Alacritech; SES2100 Accelerator card
- LeWiz Communications Inc.; Talon 3220 10 Gb Copper TCP/IP
Accel. NIC
- LeWiz Communications Inc.; Magic 2028-4P 1 Gb Copper TCP/IP
Accel. NIC
- QLogic Corp.; QLA4050C/QLA4052C iSCSI HBA
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