Basic Concepts: Linux Disks
- IDE (ATA): Bandwidth is 133 Mbps. IOPS is ~100. The interface can connect maximum 2 disks.
- SCSI: IOPS is ~ 150. It can connects 8 or 16 disks
- Ultrascsi320 - 320 MB/s
- Ultrascsi640 - 640 MB/s
- SATA: Bandwidth is 6 Gbps. IOPS is ~150. It can connects to 8 or 16 disks.
- SAS: Bandwidth is 6 Gbps. IOPS is ~200. It can connects to 8 or 16 disks.
- USB: Bandwidth is 480 MB/s. IOPS is vary.
Disk (Device) Types
Block: Can be accessed randomly. Unit is "block".
Character: Can be accessed sequentially. Unit is "character".
Disk Files (FHS)
Files are under '/dev/'. Every disk (device) is file on Linux environment.
Major: Primary device ID. To identify device type for proper drivers.
Minor: Secondary device ID. It's the entree of specific device of same type of device.
Create new device:
[root@centos] mknode /dev/usbtest b 100 231
[root@centos] ll | grep test
brw-r--r--. 1 root root 100, 231 Jul 1 11:02 usbtest
It's assigned by ICANN.
There are 3 identifications below. You also can identify disks by go to /dev/disk/by-*.
- Device file name
- Volume labels
MBR: Master Boot Record. It stars on sector 0. Size is 512 bytes. It consist of 3 parts:
- Bootloader and boot applications. Size is 446 bytes.
- Partition tables. Maximum 4 tables. 16 bytes each. Size is 64 bytes.
- MBR availability mark. '55AA' means "active". Size is 2 bytes.
The maximum 'Primary' partition tables are 4. If you need more than 4 partitions, you need to create 'Extend' partition as the last partition of the 4, then create 'Logical partitions' on top of 'Extend partition'. Labels of the 4 are start from 1 to 4. 'Logical partitions' always starts from 5.