Users Guide

10
Best practices
This section provides best practices for using MD storage arrays in VMware vSphere environments.
Defining virtual disks for vsphere
Before you provision virtual disks for VMFS datastores, you must plan how to set up storage for the ESXi
systems, including deciding on the number of virtual disks to use and the size of the virtual disks.
NOTE: For more information about making virtual disk decisions, including predictive schemes,
adaptive schemes, and disk shares, refer to the following sections of iSCSI SAN Configuration Guide:
• Using ESXi with an iSCSI Storage Area Network
• Making LUN Decisions in the VMware vSphere Online Library
When you are deciding how to format the virtual disks, keep in mind the following considerations:
• Ensure that each virtual disk has the correct RAID level and storage characteristics for applications in
the virtual machines (VMs) that use that virtual disk. Ensure that each virtual disk contains only one
VMFS datastore.
• When multiple VMs access the same VMFS datastore, use disk shares to prioritize virtual machines.
Fewer, larger virtual disks are appropriate for the following reasons:
• More flexibility to create VMs without asking the storage administrator for more space. More flexibility
for resizing virtual disks, doing snapshots, and so on. Fewer VMFS datastores to manage.
• More, smaller virtual disks are appropriate for the following reasons: Less wasted storage space.
Different applications might need different RAID characteristics.
• More flexibility, as the multipathing policy and disk shares are set per virtual disk.
• Use of Microsoft Cluster Service requires that each cluster disk resource is in its own virtual disk.
• Better performance because there is less contention for a single virtual disk.
Virtual disk decision-making schemes
When the storage characterization for a VM is not available, you can use either the predictive scheme or
the adaptive scheme to decide on the virtual disk size and number of virtual disks to use.
Using the predictive scheme to make virtual disk decisions
1. Create several virtual disks with different storage characteristics.
2. Build a VMFS Datastore on each virtual disk. Label each datastore according to its characteristics.
3. Allocate virtual disks to contain the data for VM applications in the VMFS datastores built on virtual
disks with the appropriate RAID level for the applications' requirements.
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