Tag Archives: iscsi

NexentaStor CE – an introduction

I spent some time at Christmas upgrading my home lab in preparation for the new VCAP exams which are due out in the first quarter of 2012. In particular I needed to improve my shared storage and hoped that I could reuse old h/w instead of buying something new. I’ve been using an Iomega IX2-200 for the last year but it’s performance is pretty pitiful so I usually reverted to local storage which rather defeated the purpose.

I started off having a quick look around at my storage options for home labs;

Why pick Nexenta?

I’d used OpenFiler and FreeNAS before (both are very capable) but with so much choice I didn’t have time to evaluate all the other options (Greg Porter has a few comments comparing OpenFiler vs Nexenta). Datacore and Starwind’s solutions rely on Windows rather than being bare metal (which was my preference) and I’ve been hearing positive news about Nexenta more and more recently.

On the technical front the SSD caching and VAAI support make Nexenta stand out from the crowd.

Continue reading NexentaStor CE – an introduction

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


  • 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


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

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

VCAP-DCA Study notes – 1.2 Manage Storage Capacity

Managing storage capacity is another potentially huge topic, even for a midsized company. The storage management functionality within vSphere is fairly comprehensive and a significant improvement over VI3.


  • Identify storage provisioning methods
  • Identify available storage monitoring tools, metrics and alarms

Skills and Abilities

  • Apply space utilization data to manage storage resources
  • Provision and manage storage resources according to Virtual Machine requirements
  • Understand interactions between virtual storage provisioning and physical storage provisioning
  • Apply VMware storage best practices
  • Configure datastore alarms
  • Analyze datastore alarms and errors to determine space availability

Tools & learning resources

Storage provisioning methods

There are three main protocols you can use to provision storage;

  • Fibre channel
    • Block protocol
    • Uses multipathing (PSA framework)
    • Configured via vicfg-mpath, vicfg-scsidevs
  • iSCSI
    • block protocol
    • Uses multipathing (PSA framework)
    • hardware or software (boot from SAN is h/w initiator only)
    • configured via vicfg-iscsi, esxcfg-swiscsi and esxcfg-hwiscsi, vicfg-mpath, esxcli
  • NFS
    • File level (not block)
    • No multipathing (uses underlying Ethernet network resilience)
    • Thin by default
    • no RDM, MSCS,
    • configured via vicfg-nas

I won’t go into much detail on each, just make sure you’re happy provisioning storage for each protocol both in the VI client and the CLI.

Know the various options for provisioning storage;

  • VI  client. Can be used to create/extend/delete all types of storage. VMFS volumes created via the VI client are automatically aligned.
  • CLI – vmkfstools.
    • NOTE: When creating a VMFS datastore via CLI you need to align it. Check VMFS alignment using ‘fdisk –lu’. Read more in Duncan Epping’s blogpost.
  • PowerCLI. Managing storage with PowerCLI – VMwareKB1028368
  • Vendor plugins (Netapp RCU for example). I’m not going to cover this here as I doubt the VCAP-DCA exam environment will include (or assume any knowledge of) these!

When provisioning storage there are various considerations;

  • Thin vs thick
  • Extents vs true extension
  • Local vs FC/iSCSI vs NFS
  • VMFS vs RDM

Continue reading VCAP-DCA Study notes – 1.2 Manage Storage Capacity