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Everything you need to know about vSphere and data storage

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iSCSI improvements

iSCSI storage arrays have become a popular storage choice for virtual hosts due to their lower cost and acceptable performance. Using iSCSI software initiators has always resulted in a slight performance penalty vs. hardware initiators with TCP offload engines. For vSphere, VMware rewrote the entire iSCSI software initiator stack to use CPU cycles more efficiently and to improve throughput compared to VI3.

VMware enhanced the VMkernel TCP/IP stack, optimized the cache affinity and improved internal lock efficiency. Other iSCSI improvements include easier provisioning and configuration, and support for the bi-directional Challenge Handshake Authentication Protocol (CHAP), which improves security by requiring both the initiator and target to authenticate each other.

Support for FCoE and jumbo frames

vSphere added support for newer storage and networking technologies, including:

  • Fibre Channel over Ethernet. vSphere now supports FCoE on converged network adapters (CNAs).
  • Jumbo frames. Conventional Ethernet frames are 1,518 bytes long; jumbo frames are typically 9,000 bytes, which can improve network throughput and CPU efficiency.

VMware added jumbo frame support in ESX 3.5 but didn't officially support it for use with data storage protocols. With the vSphere release, they officially support using jumbo frames with software iSCSI

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and NFS storage devices using 1 Gbps or 10 Gbps network interface cards (NICs).

Hot extend virtual disks

With VMware vSphere you can increase the size of an existing virtual disk (VMDK file) while it's powered on as long as the guest operating system supports it.

Once you increase the size of a virtual disk, the guest OS can then begin using it to create new disk partitions or to extend existing ones. Windows Server 2008, Windows Server 2003 Enterprise and Datacenter editions, and certain Linux distributions support this feature. Previously, you had to power down a VM before increasing its virtual disk size.

Grow VMFS volumes

With vSphere you can increase the size of VMFS volumes without using extents and without disrupting virtual machines. To do this in VI3, you had to join a separate logical unit number (LUN) to the VMFS volume as an extent, which had some disadvantages. vSphere lets you grow the LUN of an existing VMFS volume using your storage-area network (SAN) configuration tools and then expand the VMFS volume so it uses the additional space.

This means you don't have to use extents and can avoid moving VMs to other data stores to destroy existing VMFS volumes to create larger ones.

Pluggable Storage Architecture

VMware has given vSphere a new modular storage architecture that allows third-party vendors to interface with certain storage functionality. The Pluggable Storage Architecture (PSA) allows vendors to create plug-ins for controlling storage I/O functions like multipathing.

There's built-in functionality that allows for fixed or round-robin path selection when multiple paths to a storage device are available. Vendors can expand on this and develop their own plug-in modules for optimal performance through load balancing and more intelligent path selection. To achieve this, the PSA leverages the new capabilities provided by the vStorage APIs for multipathing.

This was first published in January 2010

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