Understanding the file system and its storage containers

How volumes are used

A volume holds user data that is accessible via one or more of the access protocols supported by Data ONTAP, including Network File System (NFS), Common Internet File System (CIFS), HyperText Transfer Protocol (HTTP), Web-based Distributed Authoring and Versioning (WebDAV), Fibre Channel Protocol (FCP), and Internet SCSI (iSCSI). A volume can include files (which are the smallest units of data storage that hold user- and system-generated data) and, optionally, directories and qtrees in a Network Attached Storage (NAS) environment, and also LUNs in a Storage Area Network (SAN) environment.

For more information about volumes, see Chapter 6, Volume Management.

How qtrees are used

A qtree is a logically-defined file system that exists as a special top-level subdirectory of the root directory within a volume. You use qtrees to manage or partition data within a volume. You can specify the following features for a qtree.

A security style like that of volumes
Whether the qtree uses CIFS oplocks
Whether the qtree has quotas (disk space and file limits)
Using quotas enables you to manage storage resources on a per user, user group, or per project status. In this way, you can customize areas for projects and keep users and projects from monopolizing resources.

For more information about qtrees, see Chapter 7, Qtree Management.

How LUNs are used

NetApp storage architecture utilizes two types of LUNs:

In SAN environments, NetApp storage systems are targets that have storage target devices, which are referred to as LUNs. With Data ONTAP, you configure the storage systems by creating traditional volumes to store LUNs or by creating aggregates to contain FlexVol volumes to store LUNs.
LUNs created on NetApp storage systems and V-Series systems in a SAN environment are used as targets for external storage that is accessible from initiators, or hosts. You use these LUNs to store files and directories accessible through a UNIX or Windows host via FCP or iSCSI.

For more information about LUNs and how to use them, see your Block Access Management Guide.
With the V-Series systems, LUNs provide external storage. They are created on the storage subsystems and are available for storage subsystems, such as IBM, HP, and Hitachi, to read data from or write data to.
With the V-Series systems, LUNs on the storage subsystem play the role of disks on a NetApp storage system so that the LUNs on the storage subsystem provide the storage instead of the V-Series system. For more information, see the V-Series Systems Planning Guide.

How files are used

A file is the smallest unit of data management. Data ONTAP and application software create system-generated files, and you or your users create data files. You and your users can also create directories in which to store files. You create volumes in which to store files and directories. You create qtrees to partition your volumes. You manage file properties by managing the volume or qtree in which the file or its directory is stored.

How to use storage resources

The following table describes the storage resources available with Data ONTAP 7.0 and later versions and how you use them.

Storage Container	Description	How to Use
Disk	Advanced Technology Attachment (ATA), Fibre Channel, or SCSI disks are used, depending on the storage system model. Some disk management functions are specific to the storage system, depending on whether the storage system uses a hardware- or software-based disk ownership method.	Once disks are assigned to a storage system, you can choose one of the following methods to assign disks to each RAID group when you create an aggregate: You provide a list of disks. You specify a number of disks and let Data ONTAP assign the disks automatically. You specify the number of disks together with the disk size and/or speed, and let Data ONTAP assign the disks automatically. Disk-level operations are described in Chapter 3, Disk and Storage Subsystem Management.
RAID group	Data ONTAP supports RAID4 and RAID-DP for all storage systems, and RAID-0 for V-Series systems. The number of disks that each RAID level uses by default is storage system model specific.	The smallest RAID group for RAID4 is two disks (one data and one parity disk); for RAID-DP, it's three (one data and two parity disks). For information about performance, see Larger versus smaller RAID groups. You manage RAID groups with the `aggr` command and FilerView. (For backward compatibility, you can also use the `vol` command for traditional volumes.) RAID-level operations are described in Chapter 4, RAID Protection of Data.
Plex	Data ONTAP uses plexes to organize file systems for RAID-level mirroring.	You can Configure and manage SyncMirror backup replication. For more information, see the Data Protection Online Backup and Recovery Guide. Split an aggregate in a SyncMirror relationship into its component plexes Rejoin split aggregates Remove and destroy plexes Change the state of a plex View the status of plexes
Aggregate	Consists of one or two plexes. A loosely coupled container for one or more FlexVol volumes. A tightly coupled container for exactly one traditional volume.	You use aggregates to manage disks, RAID groups, and plexes. You can create aggregates with the `aggr` command or with the FilerView browser interface. If you create a traditional volume, Data ONTAP automatically creates the underlying aggregate. Aggregate-level operations are described in Chapter 5, Aggregate Management.
Volume (common attributes)	Both traditional and FlexVol volumes contain user-visible directories and files, and they can also contain qtrees and LUNs.	You can apply the following volume operations to both FlexVol volumes and traditional volumes. The operations are also described in General volume operations. Changing the language option for a volume Changing the state of a volume Changing the root volume Destroying volumes Exporting a volume using CIFS, NFS, and other protocols Increasing the maximum number of files in a volume Renaming volumes The following operations are described in the Data Protection Online Backup and Recovery Guide. Implementing SnapMirror Taking snapshots of volumes Implementing the SnapLock^TM feature
FlexVol volume	A logical file system of user data, metadata, and snapshots that is loosely coupled to its containing aggregate. All FlexVol volumes share the underlying aggregate's disk array, RAID group, and plex configurations. Multiple FlexVol volumes can be contained within the same aggregate, sharing its disks, RAID groups, and plexes. FlexVol volumes can be modified and sized independently of their containing aggregate.	You can create FlexVol volumes after you have created the aggregates to contain them. You can increase and decrease the size of a FlexVol by adding or removing space in increments of 4 KB, and you can clone FlexVol volumes. FlexVol volume-level operations are described in Chapter 6, FlexVol volume operations.
Traditional volume	A logical file system of user data, metadata and snapshots that is tightly coupled to its containing aggregate. Exactly one traditional volume can exist within its containing aggregate, with the two entities becoming indistinguishable and functioning as a single unit. Traditional volumes are identical to volumes created with earlier than 7.0 versions of Data ONTAP. If you upgrade to Data ONTAP 7.0 and later versions, existing volumes are preserved as traditional volumes.	You can create traditional volumes, physically transport them, and increase them by adding disks. For information about creating and transporting traditional volumes, see Traditional volume operations. For information about increasing the size of a traditional volume, see Adding disks to aggregates.
Qtree	An optional, logically defined file system that you can create at any time within a volume. It is a subdirectory of the root directory of a volume. You store directories, files, and LUNs in qtrees. You can create up to 4,995 qtrees per volume.	You use qtrees as logical subdirectories to perform file system configuration and maintenance operations. Within a qtree, you can assign limits to the space that can be consumed and the number of files that can be present (through quotas) to users on a per-qtree basis, define security styles, and enable CIFS opportunity locks (oplocks). Qtree-level operations are described in Chapter 7, Qtree Management. Qtree-level operations related to configuring usage quotas are described in Chapter 8, Quota Management.
LUN (in a SAN environment)	Logical Unit Number; it is a logical unit of storage, which is identified by a number by the initiator accessing its data in a SAN environment. A LUN is a file that appears as a disk drive to the initiator.	You create LUNs within volumes and specify their sizes. For more information about LUNs, see your Block Access Management Guide.
LUN (with V-Series systems)	An area on the storage subsystem that is available for a V-Series system or non-V-Series system host to read data from or write data to. The V-Series system can virtualize the storage attached to it and serve the storage up as LUNs to customers outside the V-Series system (for example, through iSCSI). These LUNs are referred to as V-Series system-served LUNs. The clients are unaware of where such a LUN is stored.	See the V-Series Software Setup, Installation, and Management Guide for your storage subsystem for specific information about LUNs and how to use them for your system.
File	Files contain system-generated or user-created data. Files are the smallest unit of data management. Users organize files into directories. As a system administrator, you organize directories into volumes.	Configuring file space reservation is described in Chapter 6, Volume Management.