6.10. Devices

When using large block size (1MB), the tape driver sometimes returns an EBUSY error. To work around this problem, use a smaller block size, that is 256KB.

On some of the older Broadcom tg3 devices, the default Maximum Read Request Size (MRRS) value of 512 byte is known to cause lower performance. It is because these devices perform direct memory access (DMA) requests serially. 1500-byte ethernet packet will be broken into 3 PCIE read requests using 512 byte MRRS. When using a higher MRRS value, the DMA transfer can be faster as fewer requests will be needed. However, the MRRS value is meant to be tuned by system software and not by the driver. PCIE Base spec 3.0 section 7.8.4 contains an implementation note that illustrates how system software might tune the MRRS for all devices in the system. As a result, Broadcom modified the tg3 driver to remove the code that sets the MRRS to 4K bytes so that any value selected by system software (BIOS) will be preserved.

The Brocade BFA Fibre Channel and FCoE driver does not currently support dynamic recognition of Logical Unit addition or removal using the sg3_utils utilities (for example, the sg_scan command) or similar functionality. Please consult Brocade directly for a Brocade equivalent of this functionality.

Starting with Red Hat Enterprise Linux 6.0 and later, kexec kdump supports dumping core to the Brtfs file system. However, note that because the findfs utility in busybox does not support Btrfs yet, UUID/LABEL resolving is not functional. Avoid using the UUID/LABEL syntax when dumping core to Btrfs file systems.

The trace-cmd service does not start on 64-bit PowerPC and IBM System z systems because the sys_enter and sys_exit events do not get enabled on the aforementioned systems.

trace-cmd's subcommand, report, does not work on IBM System z systems. This is due to the fact that the CONFIG_FTRACE_SYSCALLS parameter is not set on IBM System z systems.

Red Hat Enterprise Linux 6 only has support for the first revision of the UPEK Touchstrip fingerprint reader (USB ID 147e:2016). Attempting to use a second revision device may cause the fingerprint reader daemon to crash. The following command returns the version of the device being used in an individual machine:

~]$ lsusb -v -d 147e:2016 | grep bcdDevice

The Emulex Fibre Channel/Fibre Channel-over-Ethernet (FCoE) driver in Red Hat Enterprise Linux 6 does not support DH-CHAP authentication. DH-CHAP authentication provides secure access between hosts and mass storage in Fibre-Channel and FCoE SANs in compliance with the FC-SP specification. Note, however that the Emulex driver (lpfc) does support DH-CHAP authentication on Red Hat Enterprise Linux 5, from version 5.4. Future Red Hat Enterprise Linux 6 releases may include DH-CHAP authentication.

The recommended minimum HBA firmware revision for use with the mpt2sas driver is "Phase 5 firmware" (that is, with version number in the form 05.xx.xx.xx). Note that following this recommendation is especially important on complex SAS configurations involving multiple SAS expanders.