Chapter 10. Storage

Parallel NFS (pNFS) is a part of the NFS v4.1 standard that allows clients to access storage devices directly and in parallel. The pNFS architecture can improve the scalability and performance of NFS servers for several common workloads.

pNFS defines 3 different storage protocols or layouts: files, objects and blocks. The Red Hat Enterprise Linux 6.4 NFS client supports the files layout protocol.

To enable the pNFS file-layout client in Red Hat Enterprise Linux, use the -o v4.1 option when mounting a file system on a pNFS-capable server.

When the server is pNFS-enabled, the nfs_layout_nfsv41_files kernel module is automatically loaded on the first mount. Use the following command to verify that this module was loaded:

~]$ lsmod | grep nfs_layout_nfsv41_files

For more information on pNFS, refer to http://www.pnfs.com/.

An online discard operation performed on a mounted file system discards blocks which are not in use by the file system. Online discard operations are now supported on XFS file systems. For more information, refer to the section Discard Unused Blocks in the Red Hat Enterprise Linux 6 Storage Administration Guide.

In Red Hat Enterprise Linux 6.4, LVM adds support for Micron PCIe Solid State Drives (SSDs) as devices that may form a part of a Volume Group.

LVM is now capable of creating, removing, and resizing RAID10 logical volumes. To create a RAID10 logical volume, like the other RAID types, specify the segment type as follows:

~]# lvcreate --type raid10 -m 1 -i 2 -L 1G -n lv vg

Note that the -m and -i arguments behave in the same way they would for other segment types. That is, -i is the total number of stripes while -m is the number of (additional) copies (that is, -m 1 -i 2 gives 2 stripes on top of 2-way mirrors).

Previously, to set up persistent reservations on multipath devices, it was necessary to set it up on all of the path devices. If a path device was later added, it was necessary to manually add reservations to that path. Red Hat Enterprise Linux 6.4 adds the ability to set up and manage SCSI persistent reservations through device mapper devices with the mpathpersist command. When path devices are added, persistent reservations are set up on those devices as well.