6.5.1

Table Of Contents
Table 72. Troubleshooting iSCSI LUN Display (Continued)
Troubleshooting Task Description
Check access control
configuration.
If the expected LUNs do not appear after rescan, access control might not be configured
correctly on the storage system side:
n
If CHAP is configured, ensure that it is enabled on the ESXi host and matches the storage
system setup.
n
If IP-based filtering is used, ensure that the iSCSI HBA or the VMkernel port group IP
address is allowed.
n
If you are using initiator name-based filtering, ensure that the name is a qualified iSCSI
name and matches the storage system setup.
n
For booting from a SAN, ensure that each host sees only required LUNs. Do not allow any
host to see any boot LUN other than its own. Use storage system software to make sure that
the host can see only the LUNs that it is supposed to see.
n
Ensure that theDisk.MaxLUN setting allows you to view the LUN you expect to see. For
information, see the vSphere Storage documentation.
Check storage processor setup. If a storage system has more than one storage processor, make sure that the SAN switch has a
connection to the SP that owns the LUNs you want to access. On some storage systems, only
one SP is active and the other SP is passive until a failure occurs. If you are connected to the
wrong SP (the one with the passive path) you might not see the expected LUNs, or you might
see the LUNs but get errors when trying to access them.
For software and dependent
hardware iSCSI, check network
configuration.
The software iSCSI and dependent hardware adapters in ESXi require that VMkernel network
port have access to the iSCSI storage. The adapters use the VMkernel for data transfer between
the ESXi system and the iSCSI storage.
Rescan your iSCSI initiator. Perform a rescan each time you complete the following tasks:
n
Create new LUNs on a SAN.
n
Change the LUN masking.
n
Reconnect a cable.
n
Make a change to a host in a cluster.
n
Change CHAP settings or add new discovery addresses.
For information, see the vSphere Storage documentation.
Resolving SAN Performance Problems
A number of factors can negatively affect storage performance in the ESXi SAN environment. Among
these factors are excessive SCSI reservations, path thrashing, and inadequate LUN queue depth.
To monitor storage performance in real time, use the resxtop and esxtop command-line utilities. For
more information, see the vSphere Monitoring and Performance documentation.
Excessive SCSI Reservations Cause Slow Host Performance
When storage devices do not support the hardware acceleration, ESXi hosts use the SCSI reservations
mechanism when performing operations that require a file lock or a metadata lock in VMFS. SCSI
reservations lock the entire LUN. Excessive SCSI reservations by a host can cause performance
degradation on other servers accessing the same VMFS.
vSphere Troubleshooting
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