HP xw4400 Mini White Paper
Software raid in linux workstations
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Software RAID in Linux Workstations
Mini-White Paper
Introduction......................................................................................................................................... 3
RAID Basics ........................................................................................................................................ 3
RAID Overview ................................................................................................................................ 3
Software RAID in Linux ..................................................................................................................... 3
Performance and Bottlenecks ............................................................................................................. 4
RAID Levels ......................................................................................................................................... 4
RAID-Linear: Concatenating Disks....................................................................................................... 4
RAID-0: Striping ............................................................................................................................... 4
RAID-1: Mirroring............................................................................................................................. 5
RAID-2: Error Checking and Correction .............................................................................................. 6
RAID-3: Byte-Level Striping with Parity Disk .......................................................................................... 6
RAID-4: Block-Level Striping with Parity Disk ........................................................................................ 6
RAID-5: Block-Level Striping with Distributed Parity ............................................................................... 6
Additional RAID Levels...................................................................................................................... 7
RAID Configuration Strategies ............................................................................................................... 7
Performance .................................................................................................................................... 7
Capacity versus Fault-Tolerance ......................................................................................................... 7
Cost ............................................................................................................................................... 7
RAID Performance Considerations ...................................................................................................... 8
Configuring Red Hat Enterprise Linux with Software RAID......................................................................... 8
Manual Setup of Software RAID Data Partitions..................................................................................... 11
Manual Configuration Examples.......................................................................................................... 12
RAID-0 .......................................................................................................................................... 12
RAID-1 .......................................................................................................................................... 12
RAID-5 .......................................................................................................................................... 13
RAID-10 ........................................................................................................................................ 13
Disk Failure and Recovery................................................................................................................... 14
Spare Disks and Disk Failure ........................................................................................................... 14
Multiple Disk Failure ....................................................................................................................... 15
Additional Configuration Information ................................................................................................... 15
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Summary of Contents for HP xw4400
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Page 1: Table Of Contents
Software RAID in Linux Workstations Mini-White Paper Introduction... 3 RAID Basics ... 3 RAID Overview ... 3 Software RAID in Linux ... 3 Performance and Bottlenecks ... 4 RAID Levels ... 4 RAID-Linear: Concatenating Disks... 4 RAID-0: Striping ... 4 RAID-1: Mirroring... - Page 2 The Persistent Superblock ... 15 Chunk Sizes ... 15 Swap Space in a RAID Configuration... 16 Boot Partitions in a Mirrored RAID Configuration ... 16 Software RAID and LVM ... 19...
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Page 3: Introduction
Introduction This document provides an overview of software RAID solutions for HP workstations running the Linux operating system. It assumes a basic understanding of computer hardware, filesystems, and the Linux operating system. It covers the various RAID levels, the differences between hardware RAID and software RAID, steps to configure software RAID on Linux workstations, and information regarding disk failure, recovery, and other information pertaining to running software RAID on a Linux system. -
Page 4: Performance And Bottlenecks
40GB disks configured with RAID-linear look like one 80GB disk. RAID-linear offers no practical performance or reliability gains over standard separate disks. Spare disks are not supported in RAID-linear; if one disk fails, the RAID array fails as well. RAID-linear is not supported by HP Linux workstation. -
Page 5: Raid-1: Mirroring
RAID-1. Typically performance is sacrificed for recovery of data. Because data is mirrored, only half of the physical space is utilized, and data must be replicated to multiple disks, marginally increasing write times. Software RAID-1 is supported by HP Linux workstations. Figure 2. Efficiency of Software RAID-1... -
Page 6: Raid-2: Error Checking And Correction
RAID-5 requires a minimum of 3 disks, and the effective disk space availability of n disks in a RAID-5 array is n-1 disks. Software RAID-5 is supported by HP Linux workstations. Figure 3. Efficiency of Software RAID-5... -
Page 7: Additional Raid Levels
Software RAID-10 is the only additional RAID level supported by HP Linux workstations. Please note that while the Linux kernel allows for RAID-linear, -0, -1, -4, -5, and nested RAID levels, HP only provides support for RAID-0, 1, 5, and 10. -
Page 8: Raid Performance Considerations
While it is possible to manually configure software RAID after a Linux system has been installed and configured, it is HP’s recommendation that software RAID should be configured at installation time. The Red Hat Enterprise Linux installation utility includes a configuration tool to set up software RAID partitions. - Page 9 Figure 4. Disk Partitioning Setup Select “New” to create a new partition. From the File System Type menu, choose “Software RAID.” Select one physical disk to create the partition on. Choose the size of the partition. Click OK. Figure 5. Disk Setup Repeat steps 4-8 until all necessary software RAID partitions are created.
- Page 10 Figure 6. Creating a RAID Device Choose a mount point, file system type, device, and RAID level for this partition. Figure 7. Creating a RAID Device Click OK. Continue with setup as normal. The Red Hat Enterprise Linux Anaconda installer only supports RAID-0, RAID-1, and RAID-5. Other levels or nested RAID must be configured manually after installation.
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Page 11: Manual Setup Of Software Raid Data Partitions
/boot partition on a non-RAID part of the filesystem. Manual Setup of Software RAID Data Partitions While HP recommends using the above method to set up software RAID on your Linux workstations, it is possible to manually set up a software RAID partition on multiple disks after installation. -
Page 12: Manual Configuration Examples
Most of the work in manual configuration of a software RAID array comes from the creation of the appropriate /etc/raidtab file. The following are examples of /etc/raidtab files and the corresponding mdadm commands needed to set up each of the basic RAID configurations supported by HP. RAID-0 /etc/raidtab file:... -
Page 13: Raid-5
RAID-5 /etc/raidtab file: raiddev /dev/md0 raid-level nr-raid-disks nr-spare-disks persistent-superblock chunk-size device raid-disk device raid-disk device raid-disk device raid-disk Command: mdadm -Cv /dev/md0 --level=5 --raid-devices=4 /dev/hda1 /dev/hdb1 /dev/hdc1 /dev/hdd1 RAID-10 /etc/raidtab file: raiddev /dev/md0 raid-level nr-raid-disks nr-spare-disks chunk-size device raid-disk device raid-disk raiddev /dev/md1 raid-level... -
Page 14: Disk Failure And Recovery
In a RAID-10 configuration, you will need to add three lines to the /etc/fstab file, one for each of the RAID arrays. There does not need to be a mount point specified for /dev/md0 or /dev/md1. If no mount point is specified, you will see error messages during startup, but the RAID-10 array will still initialize and mount correctly. -
Page 15: Multiple Disk Failure
Tip: You can use mdadm as a daemon to monitor a RAID array, by running: mdadm --monitor --mail=root@localhost --delay=1800 /dev/md0 This will poll the array in intervals of 1800 seconds, and critical events and failures will be emailed to the system administrator. There are many other monitoring systems available for Linux software RAID as well. -
Page 16: Swap Space In A Raid Configuration
Linux workstation. The steps to manually mirror your boot partition are outlined below: Power your HP workstation; boot to your RHEL installation media. Continue through the installation until the “Disk Partitioning Setup” screen. Select “Manually partition with Disk Druid.”... - Page 17 Figure 8. Disk Partitioning Setup On each disk that will be in the RAID-1 array, create a partition that will be bootable. One drive should have the actual /boot partition; each other drive should have a partition of the same size of format ext3.
- Page 18 Figure 9. Disk Partitioning Setup Create a RAID device by selecting the “RAID” option in the main partitioning menu, then choosing “Create a RAID Device” from the “RAID Options” screen, and configuring as desired. Continue with setup as normal. At this point, finish with the initial installation and configuration of your workstation. You should now have a partition that will be made bootable on each hard disk in the RAID array.
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Page 19: Software Raid And Lvm
Setup of the filesystem can now continue as normal. © 2006 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice. The only warranties for HP products and services are set forth in the express warranty statements accompanying such products and services.