Installation guide

iSCSI Detection and Configuration

Warning

Removing/deleting RAID metadata from disk could potentially destroy any stored data. Red Hat

recommends that you back up your data before proceeding.

To delete RAID metadata from the disk, use the following command:

dmraid -r -E /device/

For more information about managing RAID devices, refer to man dmraid and Chapter 13,

Redundant Array of Independent Disks (RAID).

iSCSI Detection and Configuration

For plug and play detection of iSCSI drives, configure them in the firmware of an iBFT boot-capable

network interface card (NIC). CHAP authentication of iSCSI targets is supported during installation.

However, iSNS discovery is not supported during installation.

FCoE Detection and Configuration

For plug and play detection of fibre-channel over ethernet (FCoE) drives, configure them in the

firmware of an EDD boot-capable NIC.

DASD

Direct-access storage devices (DASD) cannot be added/configured during installation. Such devices

are specified in the CMS configuration file.

Block Devices with DIF/DIX Enabled

DIF/DIX is a hardware checksum feature provided by certain SCSI host bus adapters and block

devices. When DIF/DIX is enabled, errors will occur if the block device is used as a general-purpose

block device. Buffered I/O or mmap(2)-based I/O will not work reliably, as there are no interlocks in the

buffered write path to prevent buffered data from being overwritten after the DIF/DIX checksum has

been calculated.

Because of this, the I/O will later fail with a checksum error. This problem is common to all block

device (or file system-based) buffered I/O or mmap(2) I/O, so it is not possible to work around these

errors caused by overwrites.

As such, block devices with DIF/DIX enabled should only be used with applications that use

O_DIRECT. Such applications should use the raw block device. Alternatively, it is also safe to use the

XFS filesystem on a DIF/DIX enabled block device, as long as only O_DIRECT I/O is issued through

the file system. XFS is the only filesystem that does not fall back to buffered IO when doing certain

allocation operations.

The responsibility for ensuring that the I/O data does not change after the DIF/DIX checksum has

been computed always lies with the application, so only applications designed for use with O_DIRECT

I/O and DIF/DIX hardware should use DIF/DIX.