The General Parallel File System (GPFS) is a cluster file system that provides concurrent access to file systems from multiple nodes. The storage provided by these nodes can be direct attached, network attached, SAN attached or a combination of these methods. GPFS provides many features beyond common data access including data replication, policy based storage management, and space efficient file snapshot and clone operations.

This driver enables the use of GPFS in a similar fashion as the NFS driver. With the GPFS driver, instances do not actually access a storage device at the block level. Instead, volume backing files are created in a GPFS file system and mapped to instances, which emulate a block device. GPFS software must be installed and running on nodes where Cinder volume and Nova compute services are running in the OpenStack environment. A GPFS file system must also be created and mounted on these nodes before starting the cinder-volume service. The details of these GPFS specific steps are covered in GPFS Administration documentation. Optionally, Glance can be configured to store images on a GPFS file system. When Cinder volumes are created from Glance images, if both image and volume data reside in the same GPFS file system, the data from image files is moved efficiently to Cinder volumes using copy on write optimization strategy.

To use Cinder with the GPFS driver, first set the volume_driver in cinder.conf: volume_driver = cinder.volume.drivers.gpfs.GPFSDriver The following table contains the configuration options supported by the GPFS driver. The flag gpfs_images_share_mode is only valid if the Image service is configured to use GPFS with gpfs_images_dir flag. Also note, when the value of this flag is copy_on_write, the paths specified by the flags gpfs_mount_point_base and gpfs_images_dir must both reside in the same GPFS file system and in the same GPFS file set.

It is possible to specify additional volume configuration options on a per-volume basis by specifying volume metadata. The volume is created using the specified options. Changing the metadata after the volume is created has no effect. The following table lists the volume creation options supported by the GPFS volume driver.

Volume Create Options for GPFS Volume Drive

Metadata Item Name	Description
fstype	The driver will create a file system or swap area on the new volume. If fstype=swap is specified, the mkswap command is used to create a swap area. Otherwise the mkfs command is passed the specified type, for example ext3, ext4, etc.
fslabel	The driver will set the file system label for the file system specified by fstype option. This value is only used if fstype is specified.
data_pool_name	The driver will assign the volume file to the specified GPFS storage pool. Note that the GPFS storage pool must already be created.
replicas	Specify how many copies of the volume file to create. Valid values are 1, 2, and, for GPFS V3.5.0.7 and later, 3. This value cannot be greater than the value of the MaxDataReplicas attribute of the file system.
dio	Enable or disable the Direct I/O caching policy for the volume file. Valid values are "yes" and "no".
write_affinity_depth	Specify the allocation policy to be used for the volume file. Note that this option only works if "allow-write-affinity" is set for the GPFS data pool.
block_group_factor	Specify how many blocks are laid out sequentially in the volume file to behave like a single large block. This option only works if "allow-write-affinity" is set for the GPFS data pool.
write_affinity_failure_group	Specify the range of nodes (in GPFS shared nothing architecture) where replicas of blocks in the volume file are to be written. See GPFS Administration and Programming Reference guide for more details on this option.

This example shows the creation of a 50GB volume with an ext4 filesystem labeled newfsand direct IO enabled: $cinder create --metadata fstype=ext4 fslabel=newfs dio=yes --display-name volume_1 50

Volume snapshots are implemented using the GPFS file clone feature. Whenever a new snapshot is created, the snapshot file is efficiently created as a read-only clone parent of the volume, and the volume file uses copy on write optimization strategy to minimize data movement. Similarly when a new volume is created from a snapshot or from an existing volume, the same approach is taken. The same approach is also used when a new volume is created from a Glance image, if the source image is in raw format, and gpfs_images_share_mode is set to copy_on_write.