Contents

Managing RAID·· 1

About RAID·· 1

Level-0 RAID·· 1

Level-1 RAID·· 1

Restrictions and guidelines: RAID management 1

Prerequisites for RAID management 2

Creating a RAID·· 2

Adding a file system to level-1 RAID·· 3

Removing a RAID·· 3

Display and maintenance commands for RAID·· 3

 

Managing RAID

About RAID

Redundant Array of Independent Disks (RAID) is a technology that uses multiple independent disks to form a large capacity disk group. This technology can store a copy of data to multiple disks so that it can store data concurrently to reduce the time for mechanically seeking storage areas. In addition, this technology improves the speed in data reading and writing.

With mirroring and storage parity information, RAID backs up data in multiple disks for high availability. Disk redundancy increases the mean time between failures, improves the reliability of data, and increases the fault tolerance.

The device supports level-0 and level-1 RAIDs that are formed by file systems. For more information about file systems, see file system management in Fundamentals Configuration Guide.

Level-0 RAID

Level-0 RAID is a disk striping technology that divides a disk into multiple strips (the minimum storage units). When the device stores a large amount of data, it divides the data into multiple blocks and concurrently spreading the data blocks across multiple strips. In this way, level-0 speeds up data storing, reading, and writing.

Level-0 RAID does not provide data redundancy. When a member disk is damaged, all data stored in the RAID will be lost. Typically, level-0 RAID is applicable to scenarios that are tolerant of low data security and availability but has strict requirements for storage performance. For example, use level-0 RAID to store video and audio data or cache temporary data.

Level-1 RAID

Level-1 RAID uses disk mirroring to ensure data reliability and repairability. While the system is writing data on the primary disk, it simultaneously mirrors the data to the backup disk. When the primary disk is damaged, the system will read data from or write data to the backup disk according to the mirroring.

Level-1 RAID is applicable to scenarios that have strict requirements in sequential read and write performance and data protection. For example, use level-1 RAID to protect data for an email system.

Restrictions and guidelines: RAID management

The device supports only one RAID at level 0 or level 1. The RAID name is fixed at md0.

·     To change the RAID level, you must first remove the current RAID. Then, create the RAID of another level.

·     If a RAID has been created on the device, you must remove that RAID before you create a new RAID.

To avoid data loss when the RAID is running correctly, do not remove member disks in the RAID. To remove a disk from the RAID:

·     For level-0 RAID, back up data in all file systems of the RAID, remove the RAID, and then remove the disk.

·     For level-1 RAID, remove the file system of the disk from the RAID, and then remove the disk.

Do not switch between the version that supports RAID and the version that does not support RAID.

All RAID management commands are supported only on the default context.

Prerequisites for RAID management

CAUTION: The partition and file system format modification operations will delete all data from a hard disk. Back up data before you perform these operations.

 

Before you configure RAID, perform the following file system tasks in user view:

1.     Back up data in all file systems that will form a RAID.

All data in the file systems will be deleted after the RAID is created. If the system fails to create the RAID, data in the file systems might also be deleted.

2.     Partition a disk if that disk has not been partitioned.

fdisk medium [ partition-number ]

An unpartitioned disk cannot join a RAID.

You cannot partition a member disk in a RAID. To partition a member disk, first remove the disk from the RAID.

3.     Mount a file system.

mount filesystem

By default, the file system of a disk is automatically mounted to the device when the disk is attached to the device.

If a file system has not been mounted to the device when you create the RAID, the system will prompt a parameter error. Before re-create the RAID, you must use the mount command to manually mount the file system to the device.

4.     Identify the size of a file system.

dir [ /all ] [ file | directory | /all-filesystems ]

To ensure RAID performance and reduce resource waste, make sure all file systems that will form the RAID have the same size.

If the sizes of the file systems are different, use the fdisk command to partition the file systems.

5.     Verify that no process is using the file systems to ensure successful RAID creation.

fuser filesystem

Partition a disk accroding to the file systems that are allowed to join a RAID. For example, the device allows only hda0:, hda1:, hdb0:, and hdb1: to join a RAID, To create a RAID, you must partition the hda or hdb disk, or both. Make sure the partitions have the same size.

For more information about disk partition, see file system management in Fundamentals Configuration Guide.

Creating a RAID

Restrictions and guidelines

·     You cannot create a RAID on an IRF fabric in the current software version.

·     After level-1 RAID is created, member disks in the RAID automatically synchronize information. If a member disk is damaged or removed, the hot backup disk added to the RAID by using the add raid command will take over the role of the damaged or removed disk. The hot backup disk will synchronize data with other disks. To avoid synchronization interruption or data loss, do not cut off the power supply or reboot the device.

Procedure

To create a RAID, execute the following command in user view:

create raid level raid-level { file-system }&<2-n>

Adding a file system to level-1 RAID

About this task

You can add a hot backup disk to level-1 RAID. When a member disk in the RAID damages, the hot backup disk can take over the role of the damaged disk to ensure correct data reading and writing.

Restrictions and guidelines

Before you add a file system to level-1 RAID, make sure the file system has been mounted to the device.

Adding a file system to level-1 RAID deletes all data from that file system.

To ensure that a file system can be added to level-1 RAID successfully, make sure the file system meets the following requirements:

·     The disk size of the file system is equal to or larger than the size of the existing disks in the RAID.

·     The file system is not used by other processes.

Procedure

To add a file system to RAID 1, execute the following command in user view:

add raid raid-name file-system

Removing a RAID

About this task

Before you remove a disk in level-1 RAID, remove the file system of that disk from the RAID. This operation avoids data loss caused by disk removal. To partition a disk in the RAID, you must first remove all disks from the RAID.

Prerequisites

Before you remove a file system from level-1 RAID, execute the display raid status command to verify that the Sync field displays Done. This operation ensures successful file system removal.To remove the entire RAID, you do not need to verify the synchronization state.

Restrictions and guidelines

You can remove a file system only from level-1 RAID. Level-0 RAID does not support file system removal.

Procedure

To remove a RAID, execute the following command in user view:

remove raid raid-name [ file-system&<1-n> ]

Display and maintenance commands for RAID

Execute display commands in any view.

 

Task	Command
Display RAID status information.	display raid status