Chapter 4. Storage

LVM Cache

As of Red Hat Enterprise Linux 7.1, LVM cache is fully supported. 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(7) manual page for information on creating cache logical volumes.
Note that the following restrictions on the use of cache logical volumes (LV):
  • The cache LV must be a top-level device. It cannot be used as a thin-pool LV, an image of a RAID LV, or any other sub-LV type.
  • The cache LV sub-LVs (the origin LV, metadata LV, and data LV) can only be of linear, stripe, or RAID type.
  • The properties of the cache LV cannot be changed after creation. To change cache properties, remove the cache and recreate it with the desired properties.

Storage Array Management with libStorageMgmt API

Since Red Hat Enterprise Linux 7.1, storage array management with libStorageMgmt, a storage array independent API, is 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. Please note that the Targetd plug-in is not fully supported and remains a Technology Preview. Supported hardware:
  • NetApp Filer (ontap 7-Mode)
  • Nexenta (nstor 3.1.x only)
  • SMI-S, for the following vendors:
    • HP 3PAR
      • OS release 3.2.1 or later
    • EMC VMAX and VNX
      • Solutions Enabler V7.6.2.48 or later
      • SMI-S Provider V4.6.2.18 hotfix kit or later
    • HDS VSP Array non-embedded provider
      • Hitachi Command Suite v8.0 or later
For more information on libStorageMgmt, refer to the relevant chapter in the Storage Administration Guide.

Support for LSI Syncro

Red Hat Enterprise Linux 7.1 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 7.1 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.

DIF/DIX Support

DIF/DIX is a new addition to the SCSI Standard and a Technology Preview in Red Hat Enterprise Linux 7.1. 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.

Enhanced device-mapper-multipath Syntax Error Checking and Output

The device-mapper-multipath tool has been enhanced to verify the multipath.conf file more reliably. As a result, if multipath.conf contains any lines that cannot be parsed, device-mapper-multipath reports an error and ignores these lines to avoid incorrect parsing.
In addition, the following wildcard expressions have been added for the multipathd show paths format command:
  • %N and %n for the host and target Fibre Channel World Wide Node Names, respectively.
  • %R and %r for the host and target Fibre Channel World Wide Port Names, respectively.
Now, it is easier to associate multipaths with specific Fibre Channel hosts, targets, and their ports, which allows users to manage their storage configuration more effectively.