Chapter 3. Storage

LIO kernel Target Subsystem

Red Hat Enterprise Linux 7 uses the LIO kernel target subsystem, which is the standard open source SCSI target for block storage, for all of the following storage fabrics: FCoE, iSCSI, iSER (Mellanox InfiniBand), and SRP (Mellanox InfiniBand).
Red Hat Enterprise Linux 6 uses tgtd, the SCSI Target Daemon, for iSCSI target support, and only uses LIO, the Linux kernel target, for Fibre-Channel over Ethernet (FCoE) targets via the fcoe-target-utils package.
The targetcli shell provides the general management platform for the LIO Linux SCSI target.

LVM Cache

Red Hat Enterprise Linux 7 introduces LVM cache as a Technology Preview. This feature allows users to create logical volumes with a small fast device performing as a cache to larger slower devices. Please refer to the lvm(8) manual page for information on creating cache logical volumes.
Note that the following commands are not currently allowed on cache logical volumes:
  • pvmove: will skip over any cache logical volume;
  • lvresize, lvreduce, lvextend: cache logical volumes cannot be resized currently;
  • vgsplit: splitting a volume group is not allowed when cache logical volumes exist in it.

Storage Array Management with libStorageMgmt API

Red Hat Enterprise Linux 7 introduces storage array management as a Technology Preview. libStorageMgmt is a storage array independent Application Programming Interface (API). It provides a stable and consistent API that allows developers to programmatically manage different storage arrays and utilize the hardware-accelerated features provided. System administrators can also use it as a tool to manually configure storage and to automate storage management tasks with the included Command Line Interface (CLI).

Support for LSI Syncro

Red Hat Enterprise Linux 7 includes code in the megaraid_sas driver to enable LSI Syncro CS high-availability direct-attached storage (HA-DAS) adapters. While the megaraid_sas driver is fully supported for previously enabled adapters, the use of this driver for Syncro CS is available as a Technology Preview. Support for this adapter will be provided directly by LSI, your system integrator, or system vendor. Users deploying Syncro CS on Red Hat Enterprise Linux 7 are encouraged to provide feedback to Red Hat and LSI. For more information on LSI Syncro CS solutions, please visit http://www.lsi.com/products/shared-das/pages/default.aspx.

LVM Application Programming Interface

Red Hat Enterprise Linux 7 features the new LVM application programming interface (API) as a Technology Preview. This API is used to query and control certain aspects of LVM.
Refer to the lvm2app.h header file for more information.

DIF/DIX Support

DIF/DIX is a new addition to the SCSI Standard and a Technology Preview in Red Hat Enterprise Linux 7. DIF/DIX increases the size of the commonly used 512-byte disk block from 512 to 520 bytes, adding the Data Integrity Field (DIF). The DIF stores a checksum value for the data block that is calculated by the Host Bus Adapter (HBA) when a write occurs. The storage device then confirms the checksum on receive, and stores both the data and the checksum. Conversely, when a read occurs, the checksum can be verified by the storage device, and by the receiving HBA.
For more information, refer to the section Block Devices with DIF/DIX Enabled in the Storage Administration Guide.

Support of Parallel NFS

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 three different storage protocols or layouts: files, objects, and blocks. The Red Hat Enterprise Linux 7 client fully supports the files layout, and the blocks and object layouts are supported as a Technology Preview.
Red Hat continues to work with partners and open source projects to qualify new pNFS layout types and to provide full support for more layout types in the future.
For more information on pNFS, refer to http://www.pnfs.com/.