5.1.1 Devices

NSS recognizes devices up to 2 TB in size (where 1 TB = 2E40 bytes = 1,099,511,627,776 bytes). The restriction for NSS is the size that the device reports to the operating system. If you have physical, logical, or virtual devices larger than 2 TB in size, you must carve them into logical devices of less than 2 TB each by using the vendor-provided or other third-party disk-carving software. For more information, see Section 10.1.1, Device Size Limit.

Storage devices can be local to the server, such as a system hard drive, or external to the server, such as with direct-attached storage or in a Fibre Channel or iSCSI storage area network (SAN). For information about common device types, see Section 10.1.2, Device Types.

A local hard drive typically contains the operating system software and can optionally be used for applications and user data.

The Linux operating system is stored on the system device by using a Linux POSIX file system (such as Ext3). By default, the system device is managed by the Linux Volume Manager 2 (LVM2), but you can configure it to be managed by EVMS by modifying the default partitioning scheme at install time. For information, see Installing with EVMS as the Volume Manager of the System Device in the OES 2 SP3: Installation Guide.

NSS data pools and volumes are supported only on devices managed by EVMS.

If your system does not have sufficient power loss protection, we require using write-through cache management for SCSI devices to minimize the risk of losing data in the event of power failure. Write-Through cache management assures the file system that writes are being committed to disk as required. For information, see Section 10.10, Enabling Write-Through Cache Management on SCSI Devices and RAID Controllers.

Understanding how much free space you will need from each device helps you during the disk carving phase of the NSS configuration. For information about space availability, see Section 10.3, Viewing a List of Devices on a Server.

For Linux, only EVMS-managed devices show up in the NSSMU and the Storage plug-in to iManager. If you use LVM2 and EVMS to manage different devices on the server, EVMS might display free space on the LVM-managed devices that EVMS cannot actually manage. For information, see Section C.3, Viewing Free Space Available to EVMS-Managed Devices.

For additional information, see Section 10.1, Understanding Devices.

5.1.2 Software RAID Devices

NSS supports software RAIDs 0, 1, 5, 10, and 15. You can RAIDS 0, 1, and 5 in iManager or in NSSMU. RAIDs 10 and 15 can be created in NSSMU.

If you use hardware RAID devices, software RAID devices are unnecessary. You can use both hardware and software RAID devices on the same server.

To maximize the performance benefits of software RAID devices, partitions used for the RAID should come from different physical devices. For software RAID 1 devices, the mirrored partitions cannot share any disks in common.

For more information, see Section 13.1, Understanding Software RAID Devices and Section 13.2, Planning for a Software RAID Device.

5.1.3 Device Partitions

NSS management tools automatically create and partitions for you on devices when you create and delete pools. For information, see Section 12.1, Understanding Partitions.

5.1.4 NSS Pools and Volumes

NSS is used for data storage on Linux. You can create NSS pools and volumes to store data on devices managed by EVMS. The operating system and applications are stored on Linux POSIX volumes.

For prerequisites for creating a pool, see Section 15.1, Guidelines for Creating a Pool.

When creating a pool, you can assign free space from multiple devices to create the maximum-sized pool of 8 TB. You can grow a pool dynamically by adding free space from the same device or different devices.

To mirror pools, each pool must use partitions from different devices; mirrored pools can have no devices in common.

Pools can contain multiple volumes, but a given volume belongs to only one pool.

Pools can be overbooked. If a pool contains multiple volumes, the cumulative administrative maximum sizes of all volumes can exceed the pool size by using the overbooking feature, although real total size is bound by physical limitations. Because space is allocated to volumes as needed, a volume might not reach its quota.

When creating a volume, assign it a fixed volume quota, or allow the volume to grow dynamically to the size of the pool. Any given volume’s quota cannot exceed the size of the pool.

For guidelines for using volume attributes, see Section 18.1, Understanding Volume Properties.

For more guidelines for creating and managing NSS volumes, see Section 18.2, Guidelines for NSS Volumes.

5.1.5 NSS Encrypted Volumes

Encrypted Volume Support is available for data volumes. Create encrypted volumes only after you verify a successful system install or upgrade. For information, see Understanding Encrypted Volume Support.

5.1.6 Storage Features

Descriptions of the NSS storage features and guidelines for their use are located in sections that discuss the how to manage them. Table 5-1 identifies the features and provides links to the guidelines.