by January 3, 2001 0 comments

Networks have become an integral part of most organizations these days. Today
more and more employees are accessing the network for Internet, intranet, other
network-based applications, or for simply sharing files across a group of
people. In such a scenario, the cost of a server shutdown can be pretty high for
an organization, as it would not only affect all the PCs connected to the server
but also the productivity of the organization. Server manufacturers are coming
out with various solutions to improve server reliability and to meet the
increasing demand of high server availability across organizations. PCI hotplug
is one step towards this.

So, what’s PCI hotplug, you may ask

PCI hotplug is an open, industry-standard technology pioneered by Compaq, and
is increasingly being used in servers these days. It’s aimed at eliminating
server downtime by making it easy to add, replace, and remove PCI cards while
the server is up and running. Products with hotplug functionality primarily
support three things: Hot replacement, Hot upgrade, and Hot expansion. Hot
replacement is the process of replacing a failed or failing PCI card without
shutting down the server. Hot upgrade is upgrading your PCI adapter card by
using either an updated PCI card or by installing the latest updated driver for
your PCI card. PCI hot expansion is nothing but adding additional PCI cards
without shutting down the server.

PCI hotplug works best when used in conjunction with other fault-tolerant
tools like RAID controllers. These tools keep the server running when a
particular device fails by automatically transferring traffic to the standby
device, and the hotplug feature lets you replace the faulty components without
shutting down the machine. For example, if the primary network interface card of
a server fails, then due to the fault-tolerant tools, the network traffic will
automatically shift to the standby or secondary NIC (Network Interface Card) and
the system will continue to run. Now, if the server supports hotplug
functionality, it will notify the administrator of the failed NIC, which can
then be replaced without shutting down the machine.

Thus, PCI hotplug improves productivity by giving you uninterrupted service.
Plus, you save time in looking around for faulty devices in your server, making
it fairly easily to manage and service various components.

Another advantage of PCI hotplug is that it’s compatible with previous PCI
standards. So any new hotplug system hardware or adapter would also work with
existing PCI-compliant systems. Also, since it’s an open industry-standard
solution, multiple vendors can implement PCI hotplug solutions, giving you a
much wider base of products to choose from.

What’s needed and how it works

To enable PCI hotplug functionality, you primarily need: a PCI hotplug-capable
server, a hotplug-aware operating system (OS) and software, software drivers for
each adapter card to support hot plugging, and a hotplug-aware user interface.

Both the hardware and software components work together to monitor the PCI
system bus to identify failed PCI cards. They also make sure that any activity,
such as adding, replacing, or upgrading a PCI card, takes place without
affecting the rest of the PCI cards on the machine. Plus, they also protect the
system from any adverse electrical effects.

When a PCI card fails, the system informs you with a system alert. You can
then use the hotplug user interface, which is nothing but a software interface,
to inform the OS of the faulty PCI card. The OS in turn instructs the hardware
to isolate or power down that particular PCI slot from the rest of the PCI
devices on that machine. (Instead of the software user interface, some machines
also make use of a push button on the slots, to inform the software to initiate
a power change).

Once the PCI slot is cut off from the rest of the devices, it can safely be
replaced with a new one. Likewise, when a new card is inserted into the PCI
slot, you can use the hotplug user interface to inform the OS of the new PCI
card. The OS then instructs the hardware to power up the slot and connect it to
the PCI bus again.

The benefits 

  1. Maximizes productivity by decreasing server downtime.

  2. Gives you uninterrupted service by letting you add, replace, and upgrade PCI cards while the server is up and running.

  3. Provides efficient, fast, and easy manageability and serviceability of components.

  4. Makes it easy to identify faulty PCI cards. Thus, you save time spent in identifying failed components. 

  5. It’s compatible with previous PCI standards, so any new hotplug system hardware will also work with the existing PCI-compliant systems.

In addition, these systems are designed such that the addition and removal of
adapter cards can take place easily. The slots have enough space between each
other. Some machines also have handles on PCI slots for fast and easy addition
and removal of PCI cards. In Compaq machines, for example, all slots are nicely
arranged together with a convenient door, and two LEDs (Light Emitting Diodes)
are placed above each PCI slot to identify their status. That is, a green light
would indicate that the PCI slot is powered on and is functioning properly and
an amber light would indicate that the slot requires attention. For further
details on compatibility issues and system hardware, read the next article ‘PCI
Hotplug in Action
’.

Today, Microsoft, SCO, Novell, Compaq, and IBM are some of the leading
vendors offering products based on this technology. Due to the increasing
popularity and the benefits associated with this technology, you can expect more
products from other leading vendors in the near future. Or, who knows, maybe
even a superior, much-advanced technology.

Neelima Vaid

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