2.6. About Primary Storage

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2.6. About Primary Storage
Primary storage is associated with a cluster and/or a zone. It stores the disk volumes for all of the VMs running on hosts in that cluster. You can add multiple primary storage servers to a cluster or a zone (at least one is required at thecluster level). Primary storage is typically located close to the hosts for increased performance. CloudStack manages the allocation of guest virtual disks to particular primary storage devices.Primary storage uses the concept of a storage tag. A storage tag is a label that is used to identify the primary storage. Each primary storage can be associated with zero, one, or more storage tags. When a VM is spun up or a data disk attachedto a VM for the first time, these tags, if supplied, are used to determine which primary storage can support the VM or data disk (ex. say you need to guarantee a certain number of IOPS to a particular volume).Primary storage can be either static or dynamic. Static primary storage is what CloudStack has traditionally supported. In this model, the administrator must present CloudStack with a certain amount of preallocated storage (ex. a volume froma SAN) and CloudStack can place many of its volumes on this storage. In the newer, dynamic model, the administrator can present CloudStack with a storage system itself (ex. a SAN). CloudStack, working in concert with a plug-in developed for that storage system,can dynamically create volumes on the storage system. A valuable use for this ability is Quality of Service (QoS). If a volume created in CloudStack can be backed by a dedicated volume on a SAN (i.e. a one-to-one mapping between a SAN volume and a CloudStackvolume) and the SAN provides QoS, then CloudStack can provide QoS.CloudStack is designed to work with all standards-compliant iSCSI and NFS servers that are supported by the underlying hypervisor, including, for example:

• SolidFire for iSCSI
  
• Dell EqualLogic™ for iSCSI
  
• Network Appliances filers for NFS and iSCSI
  
• Scale Computing for NFS
  

If you intend to use only local disk for your installation, you can skip to Add Secondary Storage.