6.1 Guidelines for NSS Storage

NSS recognizes the device sizes up to 2E64 sectors (that is, up to 8388608 petabytes (PB) based on the 512-byte sector size). For more information, see Section 11.1.1, Device Size.

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 11.1.2, Device Types.

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

If your system does not have sufficient power loss protection, you must use write-through cache management for SCSI devices to minimize the risk of losing data if there is a power failure. Write-through cache management assures the file system that writes are being committed to disk as required. For information, see Section 11.9, 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 11.2, Viewing a List of Devices on a Server.

NSS supports software RAIDs 0, 1, 5, 0+1, and 5+1. You can RAIDS 0, 1, and 5 in iManager or in NSSMU. RAIDs 0+1 and 5+1 can be created using NSSMU only.

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.

NSS software RAIDs can be used for local and clustered pools. You can use the same RAID0/5 device for multiple local pools. You can use multiple RAID0/5 devices to contribute space to a single pool. Any RAID0/5 device that is used for a clustered pool must contribute space exclusively to that pool; it cannot be used for other pools. This allows the device to fail over between nodes with the pool cluster resource. Ensure that its component devices are marked as Shareable for Clustering before you use a RAID0/5 device to create or expand a clustered pool.

For more information, see Section 14.1, Understanding Software RAID Devices and Section 14.2, Planning for a Software RAID Device.

NSS management tools automatically create and partitions for you on devices when you create and delete pools. For information, see Section 13.1, Understanding Partitions.

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

For prerequisites for creating a pool, see Section 16.1, 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.

All devices that contribute space to a clustered pool must be able to fail over with the pool cluster resource. You must use the device exclusively for the clustered pool; do not use space on it for other pools or for Linux volumes. A device must be marked as Shareable for Clustering before you can use it to create or expand a clustered pool.

For guidelines for using volume attributes, see Section 19.1, Understanding Volume Properties.

For more guidelines for creating and managing NSS volumes, see Section 19.2, Guidelines for NSS 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.

Descriptions of the NSS storage features and guidelines for their use are located in sections that discuss the how to manage them. Table 6-1 identifies the features and provides links to the guidelines.