Fabric OS Troubleshooting and Diagnostics Guide v6.4.0 (53-1001769-01, June 2010)
40 Fabric OS Troubleshooting and Diagnostics Guide
53-1001769-01
Port mirroring
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Reconciling incompatible software features
Earlier releases of software may not be supported in new versions of Fabric OS code. This may be
due to a software feature changing or new services being supported. If you suspect that you are
trying to introduce a switch into a fabric that has an older version of code, check the release notes
to verify that any features on that switch are supported in the fabric with the newer code.
When the Management Server (MS) Platform services are enabled on a switch running Fabric OS
v6.4.0 and you try to merge this switch into a fabric that does not have this feature enabled, the
switch will not merge and a segmentation occurs. To resolve this, either turn the MS Platform
services off or enable them on every switch in the fabric.
In Fabric OS v6.4.0 an ESC frame is used to exchange fabric parameters to detect Enhance TI
Zones, interoperability mode, and Virtual Fabric FID conflicts. If at any point during the ESC frame
exchange, a link with incompatible parameters is detected, the switch running Fabric OS v6.4.0
does not join into the existing fabric. To fix this issue, refer to the Fabric OS Administrator’s Guide
for more information on that specific software feature.
Port mirroring
With port mirroring, you can configure a switch port to mirror the traffic between a specific source
and destination port. This is only supported between F_Ports. This is a useful way to troubleshoot a
problem port without bringing down the host and destination links to insert an inline analyzer.
Port mirroring captures traffic between two devices. It mirrors only the frames containing the
SID/DID to the mirror port. Because of the way it handles mirroring, a single mirror port can mirror
multiple mirror connections. This also means that the port cannot exceed the maximum bandwidth
of the mirror port. Attempts to mirror more traffic than what available bandwidth allows will result in
the port mirror throttling the SID/DID traffic so that traffic does not exceed the maximum available
bandwidth.
The bandwidth of the mirror port is unidirectional. In general, a host (SID) will talk to multiple
storage devices (DIDs). Thus, a host will generally not send full line rate to a single target. A mirror
port configured at 4 Gbps can only support up to 4 Gbps of traffic. A normal 4 Gbps F_Port is
bi-directional and can support up to 8 Gbps (4 Gbps transmit and 4 Gbps receive) of traffic. If the
mirror port bandwidth is exceeded, no credits will be returned to the receiver port and thus those
devices involved in mirror connection see a degraded level of performance.
Use port mirroring to detect missing frames, which may occur with zoning issues or hold timeouts,
capture protocol errors, and capture ULP traffic (SCSI/FICON). This feature cannot be used on
embedded switch traffic.
In-Order Delivery
If IOD is enabled, adding or deleting a port mirror connection causes a frame drop. Port mirroring
basically reroutes a given connection to the mirror port. The mirror traffic takes an extra route to
the mirror port. When the extra route is removed, the frames between the two ports go directly to
the destination port. The frames at the mirror port could be queued at the destination port behind
those frames that went directly to the destination port. To prevent this IOD issue, port mirroring will
drop those frames from the mirror port when a connection is disabled. If IOD has been disabled,
port mirroring will not drop any frames, but will have an IOD error.