Linux platform: block devices, bare devices, asmlib, udev related relationships

There are two ways to access disk devices (bare partitions): 1. Character access (bare device); 2. Block mode access

Solaris platform : Under the Solaris platform, the system provides both character and block access to disk devices. Each disk has two device file names:

1. One in the/dev/dsk directory, such as/DEV/DSK/C1T1D1S1, when the device name operation, is to block the way the disk operation;
2. One in the/dev/rdsk directory, such as/DEV/RDSK/C1T1D1S1, when operating with this device name, is to operate the disk as a character (bare device mode R)

Linux platform : Under the Linux platform, the default is to provide only block device access to disk devices (such as/DEV/SDA1), without providing character access (bare device mode R). Manual configuration required for use of character access

Configure the character device (bare device) access mode	Applicable operating system version	The role of Udev
/etc/sysconfig/rawdevices +/etc/rc.local	Red Hat AS4
/etc/sysconfig/rawdevices +/etc/udev/permissions.d/50-udev.permissions	Red Hat AS4	Controlling access rights
60-raw.rules or 99-oracle-asmdevices.rules	Rhel5/oel5	Bind a block device to a bare device, a fixed device file name, and control access rights;

Linux under Platform: different ways that Oracle creates ASM in different versions :

• Before version 11.2: ASM can use disks in two ways. One is the bare device mode, and the other is the Amslib method, which allows ASM to be created on the block device.

Note: (Oracle 11.1 official) You can run ASM using Asmlib, or run ASM using raw devices.

• After version 11.2: ASM itself supports block devices directly.

Note: 11.2 Official did not find a clear explanation

• prior to version 11.2, Udev was used to bind a block device to a bare device and to control access, essentially creating an asm;11.2 version on a bare device and then using Udev as a fixed drive letter, and controlling access, essentially creating an ASM on a block device. Comparison example:

	Files read when using Udev	Udev file Contents
Before version 11.2	/etc/udev/rules.d/60-raw.rules	action== "Add", kernel== "/dev/sdb1", run+= "/bin/raw/dev/raw/raw1%N" action== "Add", kernel== "Raw1", owner= "grid", group= "Asmadmin", mode= "0660"
Version 11.2 and later	/etc/udev/rules.d/99-oracle-asmdevices.rules	kernel== "Sd*1", bus== "scsi", program== "/sbin/scsi_id-g-u-s/block/$parent", result== "sata_vbox_harddisk_ Vbd306dbe0-df3367e3_ ", name=" Asm-disk1 ", owner=" Oracle ", group=" DBA ", mode=" 0660 "

Linux platform: block devices, bare devices, asmlib, udev related relationships