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Everything you need to know about vSphere and data storage

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VMware has been a boon for system administrators, but not so much for storage pros. vSphere addresses many of the storage-related shortcomings of its predecessor.

By Eric Siebert

When VMware Inc. released vSphere in May 2009 it included more than 100 new features and enhancements, many of which addressed data storage. These data storage management enhancements include:

  • Thin provisioning enhancements
  • iSCSI improvements
  • Support for Fibre Channel over Ethernet (FCoE) and jumbo frames
  • New ability to hot extend virtual disks
  • New ability to grow VMFS volumes
  • New Pluggable Storage Architecture (PSA)
  • New paravirtualized SCSI adapters
  • New VMDirectPath for storage I/O devices
  • VMware Storage VMotion enhancements
  • New vStorage APIs
  • New storage views and alarms in vCenter Server

There are many vSphere storage enhancements and some may have a profound effect on your environment, so we'll look at each one in detail.

Thin provisioning enhancements

Thin provisioned disks are virtual disks that start small and grow as data is written to them. With a "thick" disk, all of its space is allocated when it's created; but a thin disk starts out at 1 MB (or up to 8 MB depending on the default block size) and then grows its defined maximum size as data is written to it by the

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guest OS.

Thin provisioning was available in Virtual Infrastructure 3 (VI3), but a number of changes make it more usable in vSphere:

  • Thin disks can be created using the vSphere client at the time a virtual machine (VM) is created; with VI3, the vmkfstools command line utility was used to create them.
  • Existing thick disks can be converted to thin disks using Storage VMotion while a VM is running; VI3 required powering off the virtual machine.
  • The vSphere client lets you see the actual size of thin disks (previously a command line function in VI3).
  • New configurable alarms in vCenter Server provide alerts for overallocation and usage percentages.
  • A new safety feature automatically suspends VMs with thin disks when free space is critically low.

These improvements make thin disks more manageable and much easier to use. Users often ask if they should use VMware's thin disk if their storage array supports thin provisioning ("thin-on-thin"). Use both if you can, but make sure you carefully monitor the array and VMware to ensure that you have adequate space available. Another concern with thin disks is the impact on performance as they grow and the increased fragmentation that may occur. According to VMware, thin disks have a negligible effect on performance.

This was first published in January 2010

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