2007-8-24 16:06
yddll
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Dynamic Tracking of Fibre Channel Devices
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This release provides support for Dynamic Tracking of Fibre Channel Devices.
Previous releases of AIX required a user to unconfigure FC storage device and
adapter device instances before making changes on the SAN that might result
in an N_Port ID (SCSI ID) change of any remote storage ports.
If Dynamic Tracking of FC Devices is enabled, the FC adapter driver will
detect when the Fibre Channel N_Port ID of a device changes and then re-route
traffic destined for that device to the new address while the devices are
still online. Examples of events that can cause an N_Port ID to change are
moving a cable between a switch and storage device from one switch port to
another, connecting two separate switches via an Inter-Switch Link (ISL),
and possibly rebooting a switch.
Dynamic Tracking of FC devices is controlled by a new fscsi device attribute,
'dyntrk'. The default setting for this attribute is 'no'. Setting this
attribute to 'yes', as shown in the example
chdev -l fscsi0 -a dyntrk=yes
(assuming fscsi device instance is fscsi0), enables dynamic tracking.
Dynamic Tracking logic is invoked when the adapter driver receives an
indication from the switch that there has been a link event involving a
remote storage device port.
The requirements for Dynamic Tracking support are the same as those for
"Fast I/O Failure for Fibre Channel Devices" and also include the following
requirements:
- Dynamic Tracking requires that device World Wide Name (Port Name) and
Node Names remain constant, and that World Wide Name be unique.
Changing the World Wide Name or Node Name of an available or on-line device
could result in I/O failures.
In addition, each FC storage device instance must have world_wide_name
and node_name attributes. Updated filesets that contain the 'sn_location'
attribute mentioned in the next bullet should also be updated to contain
both of these attributes.
- The storage device must provide a reliable method to extract a unique serial
number for each LUN. The AIX FC device drivers will not autodetect serial
number location, so the method for serial number extraction must be
explicitly provided by any storage vendor in order to support
dynamic tracking for their devices. This information is conveyed to the
drivers via the 'sn_location' ODM attribute for each storage
device. If the disk or tape driver detects that the 'sn_location'
ODM attribute is missing, an error log of type INFO will be generated and
dynamic tracking will NOT be enabled.
Note: The 'sn_location' attribute may be non-displayable, so
running the 'lsattr' command on an hdisk, for example, may not show
the attribute, but it may, indeed, be present in ODM.
- The FC device drivers will be able to track devices on a SAN fabric, where
a SAN fabric is defined as a fabric as seen from a single host bus adapter,
if the N_Port IDs on the fabric stabilize within about 15 seconds.
If cables are not reseated or N_Port IDs continue to change after the
initial 15 seconds, I/O failures could result.
- Devices will not be tracked across host bus adapters. Devices will only
track if they remain visible from the same HBA that they were originally
connected to.
For example, if device A were moved from one location to another on fabric A
attached to host bus adapter A (i.e., its N_Port on fabric A changes), the
device would seamlessly be tracked without any user intervention and I/O
to this device can continue.
However, if a device A is visible from HBA A but not from HBA B,
and device A is moved from the fabric attached to HBA A to the fabric
attached to HBA B, device A will not be accessible on fabric A nor on
fabric B. User intervention would be required to make it available on
fabric B by invoking cfgmgr. The AIX device instance on fabric A would no
longer be usable, and a new device instance on fabric B would be created.
This device would have to manually be added to volume groups, multipath
device instances, etc. In essence, this is the same as removing a device
from fabric A and adding a new device to fabric B.
- No dynamic tracking will performed for FC dump devices while an AIX
system dump is in progress. In addition, dynamic tracking is not supported
during boot or during cfgmgr invocations. SAN changes should not be made
while any of these operations are in progress.
- Once devices are tracked, ODM will potentially contain stale information as
SCSI IDs in ODM will no longer reflect actual SCSI IDs on the SAN. ODM will
remain in this state until cfgmgr is run manually or the system is
rebooted, provided all drivers, including any third party FC SCSI target
drivers, are dynamic-tracking capable. If cfgmgr is run manually, cfgmgr
must be invoked on all affected fscsi devices, which can easily be
accomplished by running cfgmgr without any options, or by invoking
cfgmgr on each fscsi device individually.
Note: Running cfgmgr at run time to recalibrate the SCSI IDs may not
update the SCSI ID in ODM for a storage device if the storage device is
currently opened, such as when volume groups are varied on.
cfgmgr would need to be run on devices that are not opened or the system
should be rebooted to recalibrate the SCSI IDs. Note that stale SCSI IDs
in ODM have no adverse affect on the FC drivers and recalibration of
SCSI IDs in ODM is not necessary for the FC drivers to function properly.
Any applications that communicate with the adapter driver directly via
ioctl calls and use the SCSI ID values from ODM, however, need to be
updated as indicated in the next bullet to avoid using potentially
stale SCSI IDs.
- All applications and kernel extensions that communicate with the FC Adapter
Driver, either via ioctl calls or directly to the FC driver's entry points,
must support the version 1 ioctl and scsi_buf APIs of the FC Adapter
Driver in order to work properly with FC dynamic tracking. Non-compliant
applications or kernel extensions may not function properly and/or fail
after a dynamic tracking event. If the FC adapter driver detects an
application or kernel extension that is not adhering to the new version 1
ioctl and/or scsi_buf API, an error log of type INFO will be generated and
dynamic tracking may not be enabled for the device that this application/
kernel extension may be trying to communicate with.
ISVs developing kernel extensions and/or applications that communicate with
the AIX Fibre Channel Driver stack should refer to the "Fibre Channel
Protocol for SCSI and iSCSI Subsystem" article in "AIX 5L Version 5.2 Kernel
Extensions and Device Support Programming Concepts" (pay special attention
to the "Required FCP and iSCSI Adapter Device Driver ioctl Commands" and
"Understanding the scsi_buf Structure sections") for changes necessary
to support Dynamic Tracking.
- Even with dynamic tracking enabled users are strongly encouraged to make
SAN changes, such as cable moves/swaps and establishing ISL links, during
maintenance windows. Making SAN changes during full production runs is
discouraged. This is due to the fact that there is a short interval of
time to perform any SAN changes. Cables that are not reseated correctly,
for example, could result in I/O failures. Performing these operations
during a time of little/no traffic minimizes impact of I/O failures due to
misplugging of cables, taking too long to recable, etc.
At the time of this release, the base AIX FC SCSI Disk and FC SCSI Tape
device drivers support dynamic tracking.
For status on dynamic tracking support for the FAStT product line,
refer to the following URLs:
IBM FAStT Storage Manager v7.10:
[url]http://www-3.ibm.com/pc/support/site.wss/MIGR-40711.html[/url]
IBM FAStT Storage Manager v8.21:
[url]http://www-3.ibm.com/pc/support/site.wss/MIGR-43839.html[/url]
IBM FAStT Storage Manager v8.3:
[url]http://www-3.ibm.com/pc/support/site.wss/MIGR-50177.html[/url]
After accepting the license agreement, proceed to the link for
Storage Manager for AIX. Look for the current version of this
software and follow the link to the associated README. Product
support and enhancement announcents will be made here. These
announcements should contain information on what AIX APARs are
required to support dynamic tracking on FAStT.
In addition, the IBM ESS, EMC Symmetrix and HDS storage devices support
dynamic tracking provided that the vendor provides the ODM filesets with
the necessary 'sn_location' and 'node_name' attributes. Contact the
storage vendor if you are not sure if your current level of ODM fileset
supports dynamic tracking.
If vendor-specific ODM entries are not being used for the storage device,
but the ESS, Symmetrix or HDS storage subsystem is configured with the
displayable message of "MPIO Other FC SCSI Disk", then dynamic tracking
is supported for these devices in this configuration.
The STK tape device using the standard AIX device driver also supports
dynamic tracking provided the STK fileset contains the necessary
'sn_location' and 'node_name' attributes.
Note: It is strongly recommended that SAN changes involving tape devices
be made with no active I/O. Due to the serial nature of tape devices,
a single I/O failure can cause an application, such as a tape backup,
to fail.
Devices that configure with the displayable messages of "Other FC SCSI Disk"
or "Other FC SCSI Tape" will not support dynamic tracking.