VCAP-DCA Study guide – 6.4 Troubleshooting Storage Performance and Connectivity

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Knowledge

  • Recall vicfg-* commands related to listing storage configuration
  • Recall vSphere 4 storage maximums
  • Identify logs used to troubleshoot storage issues
  • Describe the VMFS file system

Skills and Abilities

  • Use vicfg-* and esxcli to troubleshoot multipathing and PSA‐related issues
  • Use vicfg-module to troubleshoot VMkernel storage module configurations
  • Use vicfg-* and esxcli to troubleshoot iSCSI related issues
  • Troubleshoot NFS mounting and permission issues
  • Use esxtop/resxtop and vscsiStats to identify storage performance issues
  • Configure and troubleshoot VMFS datastores using vmkfstools
  • Troubleshoot snapshot and resignaturing issues

Tools

There’s obviously a large overlap between diagnosing performance issues and tuning storage performance, so check section 3.1 in tandem with this objective.

Recall vicfg-* commands related to listing storage configuration

  • vicfg-scsidevs
  • vmkiscsi-tool
  • vicfg-mpath
  • vicfg-iscsi
  • esxcli corestorage | nmp | swiscsi
  • vicfg-nas
  • showmount -e
  • esxtop/resxtop
    • look for CONS/s – this indicates SCSI reservation conflicts and might indicate too many VMs in a LUN. This field isn’t displayed by default (press ‘f’ then ‘f’ again to add it)
  • vscsiStats
  • vmkfstools
  • vicfg-module

Storage Maximums

Refer to section 1.2, Storage Capacity or read VMware’s vSphere Maximum’s white paper.

Identify logs used to troubleshoot storage issues

  • /var/log/vmKernel (ESX only)
  • /var/log/messages
  • /var/log/dmesg
  • /var/log/vmkscsid.log
  • /var/log/vmware/vpxa/vpxa.log
  • /var/log/hostd/hostd.log
  • vCenter logs
  • Use tail -f to watch /var/log/vmkernel to monitor a svMotion

Describe the VMFS file system

I suspect this objective is carried over from the VI 3.5 Enterprise exam, and hence a good place to check is these Enterprise 3.5 study notes. There’s also a useful recent blogpost by Deinos Cloud.

Be aware of VMFS alignment – Vaughn Stewart’s latest blogpost

Use vicfg-* and esxcli to troubleshoot multipathing and PSA‐related issues

Refer to section 1.3.

Use vicfg-module to troubleshoot VMkernel storage module configurations

Refer to section 9.1, advanced ESX builds.

Use vicfg-* and esxcli to troubleshoot iSCSI related issues

There are various ways to configure iSCSI at the command line;

  • vicfg-iscsi – the most powerful CLI tool as it can configure pretty much anything – targets, host adapters, authentication, etc
  • esxcli swiscsi – typically used to configure multipathing for iSCSI. See section 1.1 for details.
  • esxcfg-swiscsi – can enable, disable, and query status of iSCSI but not much more.
  • esxcfg-hwiscsi – can enable, disable, and query status of iSCSI but not much more.

Things to check;

  • Are any LUNs masked? (see section 1.1)
  • Which HBAs are available?
    vicfg-iscsi –H -l
  • Are the expected number of paths available?
    vicfg-mpath -l
  • Are the targets correctly configured?
    vicfg-iscsi –T –l vmhba33
  • Are the LUNs correctly configured?
    vicfg-iscsi –L –l vmhba33
  • Is authentication correctly configured?
    vicfg-iscsi –A –l vmhba33

Troubleshoot NFS mounting and permission issues

There’s a good video on this in the Trainsignal Troubleshooting Course, but in reality there’s not much to check inside VMware – permissions are handled on the storage array or NAS server.

  • Use vmkping to ensure the vmKernel has connectivity to the NAS server
  • esxcfg-nas –l’ to show configured NFS datastores
  • For ESX hosts you may be able to use the SC to diagnose permissions issues;
    • Ensure the nfsClient service is enabled on the firewall (esxcfg-firewall –e nfsClient)
    • Ensure the service console can see the storage target using ping (the target may be on an isolated network as per best practices)
    • Use ‘showmount –e <IP of storage array>’ (showmount –e 192.168.215.33)
Diagnosing NFS permissions at the service console

Use esxtop/resxtop and vscsiStats to identify storage performance issues

Refer to section 3.5.

Configure and troubleshoot VMFS datastores using vmkfstools

Refer to section 1.2.

Troubleshooting snapshots and resignaturing

Use vmware-cmd;

vmware-cmd /vmfs/volumes/LocalRAID5/testVM/testVM.vmx hassnapshot

For resignaturing refer to section 1.1.

Further Reading

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