HP Xw9400 Software RAID in Linux Workstations - Page 16

Swap Space in a RAID Configuration, Boot Partitions in a Mirrored RAID Configuration

Get HP Xw9400 - Workstation - 16 GB RAM PDF manuals and user guides View all HP Xw9400 manuals
Add to My Manuals
Save this manual to your list of manuals

Page 16 highlights

Chunk sizes must be specified for all RAID levels, including linear mode. However, the chunk size does not make any difference for RAID-Linear. The argument to the chunk-size option in the /etc/raidtab file specifies the chunk size in kB, so "4" means "4kB." For optimal performance, you should experiment with the value, as well as with the block-size of the filesystem you put in the array. Swap Space in a RAID Configuration There is generally no need to use RAID for swap performance. The kernel itself can stripe the swap space over multiple physical disks, provided each stripe is given the same priority in the /etc/fstab file. For example, the /etc/fstab file for striping the swap space over three drives might look like the following: /dev/sda2 swap swap defaults,pri=1 0 0 /dev/sdb2 swap swap defaults,pri=1 0 0 /dev/sdc2 swap swap defaults,pri=1 0 0 This will allow the machine to swap in parallel over multiple physical devices. The Linux kernel itself has this capability; there is no need for RAID implementation of swap space. Boot Partitions in a Mirrored RAID Configuration The mirroring for Linux in software RAID configuration is the mirroring of partitions, not physical drives. For this reason, the Master Boot Record (MBR) is not mirrored in a RAID-1 configuration, and therefore, the mirrored drive or drives are not inherently bootable. Currently there is no way to mirror the boot partition of a hard drive using utilities such as Disk Druid, so the mirrored drives must be configured manually in order to make them bootable by Linux in case the first drive fails. One possible configuration for a software RAID-1 array in Linux is to install the /boot partition on a separate physical hard disk from the rest of the filesystem. For example, /dev/sda1 would be a hard disk containing the /boot partition, and /dev/sdb1 and /dev/sdc1 would be separate physical disks making up the / partition, configured in a RAID-1 array that is independent of the /boot partition. In this case, failure of one of the hard disks in the RAID array would not affect the disk with the /boot partition. If placing the / and /boot partitions on separate physical drives as described above is not possible or desirable, more manual configuration is required to make sure that all hard drives in a RAID-1 array will be bootable in case of failure. In this case, you will need to create a bootable partition on each physical hard disk that will be part of the RAID-1 array. This is easiest when done during the original installation and configuration of the Linux workstation. The steps to manually mirror your boot partition are outlined below: 1. Power your HP workstation; boot to your RHEL installation media. 2. Continue through the installation until the "Disk Partitioning Setup" screen. 3. Select "Manually partition with Disk Druid." 16

  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10
  • 11
  • 12
  • 13
  • 14
  • 15
  • 16
  • 17
  • 18
  • 19
Chunk sizes must be specified for all RAID levels, including linear mode. However, the chunk size
does not make any difference for RAID-Linear. The argument to the
chunk-size
option in the
/etc/raidtab
file specifies the chunk size in kB, so “4” means “4kB.”
For optimal performance, you should experiment with the value, as well as with the block-size of the
filesystem you put in the array.
Swap Space in a RAID Configuration
There is generally no need to use RAID for swap performance. The kernel itself can stripe the swap
space over multiple physical disks, provided each stripe is given the same priority in the
/etc/fstab
file. For example, the
/etc/fstab
file for striping the swap space over three drives
might look like the following:
/dev/sda2
swap
swap
defaults,pri=1
0 0
/dev/sdb2
swap
swap
defaults,pri=1
0 0
/dev/sdc2
swap
swap
defaults,pri=1
0 0
This will allow the machine to swap in parallel over multiple physical devices. The Linux kernel itself
has this capability; there is no need for RAID implementation of swap space.
Boot Partitions in a Mirrored RAID Configuration
The mirroring for Linux in software RAID configuration is the mirroring of partitions, not physical
drives. For this reason, the Master Boot Record (MBR) is not mirrored in a RAID-1 configuration, and
therefore, the mirrored drive or drives are not inherently bootable. Currently there is no way to mirror
the boot partition of a hard drive using utilities such as Disk Druid, so the mirrored drives must be
configured manually in order to make them bootable by Linux in case the first drive fails.
One possible configuration for a software RAID-1 array in Linux is to install the
/boot
partition on a
separate physical hard disk from the rest of the filesystem. For example,
/dev/sda1
would be a
hard disk containing the
/boot
partition, and
/dev/sdb1
and
/dev/sdc1
would be separate
physical disks making up the
/
partition, configured in a RAID-1 array that is independent of the
/boot
partition. In this case, failure of one of the hard disks in the RAID array would not affect the
disk with the
/boot
partition.
If placing the
/
and
/boot
partitions on separate physical drives as described above is not possible
or desirable, more manual configuration is required to make sure that all hard drives in a RAID-1
array will be bootable in case of failure. In this case, you will need to create a bootable partition on
each physical hard disk that will be part of the RAID-1 array. This is easiest when done during the
original installation and configuration of the Linux workstation.
The steps to manually mirror your boot partition are outlined below:
1.
Power your HP workstation; boot to your RHEL installation media.
2.
Continue through the installation until the “Disk Partitioning Setup” screen.
3.
Select “Manually partition with Disk Druid.”
16