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To derive maximal benefit from system virtualization, storage virtualization, as implemented in a SAN, is a necessary prerequisite. The mobility of a virtual machine (VM) and its data plays an important role in daily operational tasks from load balancing with VMotion™ and VMware Distributed Resource Manager (DRS) to system testing. The issues of availability and mobility really rise to the forefront in a disaster recovery scenario: The image of files stranded on a server that is not functional does not make a great poster for high availability. Seldom an issue in datacenters, harnessing the holistic synergies of system and storage virtualization is often a major hurdle for IT at smaller companies or remote branch locations without a SAN in place. To remove that stumbling block, LeftHand Networks has introduced their Virtual SAN Appliance (VSA) for VMware® ESX. In a few simple steps, a system administrator can employ two or more VSAs, to create a fully redundant iSCSI SAN using previously isolated direct attached storage on ESX servers.
Infrastructure virtualization became a critical focus area for CIOs because it eliminates the constraints of physical limitations from IT devices. Once a resource's function is separated from its physical implementation, that resource can be placed into a generic pool, which can be managed as a single functional entity. That opens significant opportunities to reduce IT operating costs through more efficient resource utilization. In particular, administrators can configure OS and applications software as a template to simplify and standardize the provisioning of system configurations. More importantly, storage virtualization in a VMware Virtual Infrastructure (VI) environment is far less complex than storage virtualization in a typical FC SAN with physical systems. A standard OS, such as Microsoft® Windows and Linux®, assumes exclusive ownership of storage volumes. For that reason, the file systems for a standard OS does not incorporate a distributed lock manager (DLM), which is essential, if multiple systems are to maintain a consistent view of a volume's contents. That makes volume ownership a critical part of storage virtualization and explains why SAN management is the exclusive domain of storage administrators at most enterprise-class sites.
This is not the case for servers running ESX. The file system for ESX, dubbed VMFS, handles distributed file locking, which eliminates exclusive volume ownership as a burning issue.What's more, the files in a VMFS volume are single-file images of a VM disk—making them loosely analogous to an ISO formatted CDROM.When a VM mounts a disk, it opens a disk-image file; VMFS locks that file; and the VM gains exclusive ownership of the disk volume.
With volume ownership issue moot, iSCSI becomes a perfect way to extend the benefits of physical and functional separation via a cost-effective lightweight SAN. That’s made iSCSI de rigueur in large datacenters for ESX servers, for which a SAN is essential to leverage all the advanced features of a VMware Virtual Infrastructure (VI) environment. Storage administrators only need to provision iSCSI concentrators or routers with bulk storage from a Fibre Channel SAN. ESX system administrators can easily address the remaining iSCSI and ESX issues.
LeftHand Networks’Virtual SAN Appliance (VSA) opens the door for SMB and remote office sites to create and manage a secure, cost-effective, and fail-safe iSCSI SAN by simply leveraging existing direct attached storage (DAS) on ESX Servers.Moreover, for cost-conscious risk-averse IT decision makers, there are two critical distinctions for the LeftHand Networks VSA:
1. This VMware appliance is a version of SAN/IQ®: a storage software platform built on the Linux Kernel: It is not as an application running on a commercial OS that requires an additional license.
2. The LeftHand Networks appliance is designed to be clustered using multiple ESX servers in order to withstand the loss of one or more servers.
To support a VMware VI environment, openBench Labs set up two quadprocessor servers, a Dell® PowerEdge™ 1900 and an HP ProLiant DL580 G3, as our core ESX servers. These servers would run multiple VMs with either Windows Server® 2003 SP2 or Novel SUSE® Linux Enterprise Server 10 SP1 as their OS. For our initial SAN/IQ cluster, we ran a LeftHand VSA on our Dell PowerEdge 1900 and an HP Proliant ML350 G3. Each VSA gets its functionality by running the latest version of the LeftHand SAN/IQ storage software platform within a VM. Our test scenarios focused on easy of use, performance, and failover with two and three VSAs forming a cluster.
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