System information

Disaster recovery
Having all data stored on a SAN facilitates the remote storage of data backups.
You can restart virtual machines on remote ESX/ESXi hosts for recovery if one
site is compromised.
Simplified array
migrations and storage
upgrades
When you purchase new storage systems or arrays, use storage VMotion to
perform live automated migration of virtual machine disk files from existing
storage to their new destination.
Finding Further Information
In addition to this document, a number of other resources can help you configure your ESX/ESXi system in
conjunction with a SAN.
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Use your storage array vendor's documentation for most setup questions. Your storage array vendor might
also offer documentation on using the storage array in an ESX/ESXi environment.
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The VMware Documentation Web site.
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The iSCSI SAN Configuration Guide discusses the use of ESX/ESXi with iSCSI storage area networks.
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The VMware I/O Compatibility Guide lists the currently approved HBAs, HBA drivers, and driver versions.
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The VMware Storage/SAN Compatibility Guide lists currently approved storage arrays.
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The VMware Release Notes give information about known issues and workarounds.
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The VMware Knowledge Bases have information on common issues and workarounds.
Understanding VMFS Datastores
To store virtual disks, ESX/ESXi uses datastores, which are logical containers that hide specifics of storage from
virtual machines and provide a uniform model for storing virtual machine files. Datastores that you deploy
on storage devices use the VMware Virtual Machine File System (VMFS) format, a special high-performance
file system format that is optimized for storing virtual machines.
A VMFS datastore can run multiple virtual machines as one workload. VMFS provides distributed locking for
your virtual machine files, so that your virtual machines can operate safely in a SAN environment where
multiple ESX/ESXi hosts share a set of LUNs.
Use the vSphere Client to set up a VMFS datastore in advance on any SCSI-based storage device that your ESX/
ESXi host discovers. A VMFS datastore can be extended over several physical storage extents, including SAN
LUNs and local storage. This feature allows you to pool storage and gives you flexibility in creating the storage
volume necessary for your virtual machine.
You can increase the capacity of a datastore while virtual machines are running on the datastore. This ability
lets you add new space to your VMFS datastores as your virtual machine requires it. ESX/ESXi VMFS is
designed for concurrent access from multiple physical machines and enforces the appropriate access controls
on virtual machine files.
Sharing a VMFS Datastore Across ESX/ESXi Hosts
As a cluster file system, VMFS lets multiple ESX/ESXi hosts access the same VMFS datastore concurrently.
To ensure that multiple servers do not access the same virtual machine at the same time, VMFS provides on-
disk locking. To coordinate access to VMFS internal file system information, ESX/ESXi uses SCSI reservations
on the entire LUN.
Figure 2-1 shows several ESX/ESXi systems sharing the same VMFS volume.
Fibre Channel SAN Configuration Guide
18 VMware, Inc.