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PCI Hotplug for Servers

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PCQ Bureau
New Update

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.

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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.

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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

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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).

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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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