Chapter 25. Storage

Red Hat Enterprise Linux 7.2 includes a new multiple-queue I/O scheduling mechanism for block devices known as blk-mq. The scsi-mq package allows the Small Computer System Interface (SCSI) subsystem to make use of this new queuing mechanism. This functionality is provided as a Technology Preview and is not enabled by default. To enable it, add scsi_mod.use_blk_mq=Y to the kernel command line.

lvmlockd is a next generation locking infrastucture for LVM. It allows LVM to safely manage shared storage from multiple hosts, using either the dlm or sanlock lock managers. sanlock allows lvmlockd to coordinate hosts through storage-based locking, without the need for an entire cluster infrastructure. For more information, see the lvmlockd(8) man page.

Since Red Hat Enterprise Linux 7.1, storage array management with libStorageMgmt, a storage array independent API, has been fully supported. The provided API is stable, consistent, and allows developers to programmatically manage different storage arrays and utilize the hardware-accelerated features provided. System administrators can also use libStorageMgmt to manually configure storage and to automate storage management tasks with the included command-line interface.

The Targetd plug-in is not fully supported and remains a Technology Preview.

DIF/DIX is a new addition to the SCSI Standard. It is fully supported in Red Hat Enterprise Linux 7.2 for the HBAs and storage arrays specified in the Features chapter, but it remains in Technology Preview for all other HBAs and storage arrays.

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 receipt, 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.