Network Shared Disk (NSD) creation considerations
You must prepare each physical disk you intend to use with GPFS by first defining it as a Network Shared Disk (NSD) using the mmcrnsd command.
On Windows, GPFS will only create NSDs from empty disk drives. mmcrnsd accepts Windows Basic disk or Unknown/Not Initialized disks. It always re-initializes these disks so that they become Basic GPT Disks with a single GPFS partition. NSD data is stored in GPFS partitions. This allows other operating system components to recognize that the disks are used. mmdelnsd deletes the partition tables created by mmcrnsd.
A new NSD format was introduced with GPFS 4.1. The new format is referred to as NSD v2, and the old format is referred to as NSD v1. The NSD v1 format is compatible with GPFS releases prior to 4.1. The latest GPFS release recognizes both NSD v1 and NSD v2 formatted disks.
- On Linux, includes a partition table so that the disk is easily recognized as a GPFS device
- Adjusts data alignment to support disks with a 4 KB physical block size
- Adds backup copies of some key GPFS data structures
- Expands some reserved areas to allow for future growth
Administrators do not need to select one format or the other when managing NSDs. GPFS will always create and use the correct format based on the minReleaseLevel for the cluster and the file system version. When minReleaseLevel (as reported by mmlsconfig) is less than 4.1.0.0, mmcrnsd will only create NSD v1 formatted disks. When minReleaseLevel is at least 4.1.0.0, mmcrnsd will only create NSD v2 formatted disks. In this second case, however, the NSD format may change dynamically when the NSD is added to a file system so that the NSD is compatible with the file system version.
On Linux, NSD v2 formatted disks include a GUID Partition Table (GPT) with a single partition. The GPT allows other operating system utilities to recognize when a disk is owned by GPFS, which helps prevent inadvertent data corruption. After running mmcrnsd, Linux utilities like parted can show the partition table. When an NSD v2 formatted disk is added to a 3.5 or older file system, its format is changed to NSD v1 and the partition table is converted to an MBR (MS-DOS compatible) type.