HP X.25/9000 User's Guide HP-UX 11i v3 (5900-1523, August 2011)

Card compatibility
On-line addition
When on-line adding an interface card, the first issue that must be resolved is whether the new
card is compatible with the system. Each OLA/R-capable PCI slot provides a set amount of power.
The replacement card cannot draw more power than is available.
The card must also operate at the slot’s bus frequency. A PCI card must run at any frequency lower
than its maximum capability, but a card that could only operate at 33 MHz would not work on a
bus running at 66 MHz. rad provides information about the bus frequency and power available
at a slot, as well as other slot-related data.
On-line replacement
When on-line replacing an interface card, the replacement card must be identical to the card being
replaced. This is referred to as like-for-like replacement and should be adhered to because using
a similar but not identical card may cause unpredictable results. For example, a newer version of
the target card which is identical in terms of hardware may contain an updated firmware version
that could potentially conflict with the current driver.
The PCI specification allows a single physical card to contain more than one function. A
single-function SCSI bus adapter cannot be replaced by a dual-function adapter, even if the
additional function on the card was identical to the original SCSI bus adapter.
When the replacement card is added to the system, the appropriate driver for that card must be
configured in the kernel before beginning the operation. SMH ensures the correct driver is present.
(In most cases, the replacement card will be the same type as a card already in the system, and
this requirement will be automatically met.) If you have any question about the driver’s presence,
or if you are not certain that the replacement card is identical to the existing card, you can use
ioscan together with rad to investigate.
• During the replacement process, the original driver instance runs in a suspended state. I/O
to the card is either queued or failed while the card is suspended. When the replacement
card is brought on-line, the driver instance resumes normal operation. The driver instance must
be capable of resuming and controlling the replacement card.
• If the necessary driver is not present and the driver is a dynamically loadable kernel module
(DLKM), you can load it manually.
• If the driver is static and not configured in the kernel, then the card cannot be On-line Added.
The card could be physically inserted on-line, but no driver would claim it.
Critical resources
Replacing a card that is still operating can have extensive ramifications. Since power to the slot
must be off when the old card is removed and the new card is inserted, the effects of shutting down
the card’s functions must be considered.
This is particularly important if there is no on-line failover or backup card to pick up those functions.
For example:
• Which mass storage devices will be temporarily disconnected when the card is shut down?
• Will a critical networking connection be lost?
A critical resource is one that would cause a system crash or prevent the operation from successfully
completing if the resource were temporarily suspended or disconnected. For example, if the SCSI
adapter to be replaced connects to the unmirrored root disk or swap space, the system will crash
when the card is shut down.
During an OLA/R procedure, it is essential to check the targeted card for critical resources, as well
as the effects of existing disk mirrors and other situations where a card’s functions can be taken
over by another card that will not be affected.
72 OLA/R overview and concepts