User:Az990tony/edublog-beta-sw

This software stack is based on This Beta Server hardware built for the Educational Blogger Project .

Devices Available

Based on the hardware, the following devices are available:

CD/DVD Burner

/dev/hda (it is in the Primary/Master position on the first EIDE cable)

/dev/cdrom (many operating systems use this)

/dev/dvd (and this)

/dev/dvdrw (and this)

SATA disks

/dev/sda (this is drive 1)

/dev/sdb (this is drive 2)

Note that /dev/sda1, sda2, sda3 and sda4 can be bootable primary partitions. Typically, sda4 is configured as an "extended partition" which allows subsets to be defined as logical partitions sda5, sda6, and so on.

USB keys or external drives

/dev/sdf for the drive itself

/dev/sdf1 (for the VFAT file system usually on it)

Ethernet Network Interface cards

eth0, eth1 and eth2 seemed to be assigned to the one motherboard connector and two PCI cards differently between operating systems. I will need to track down the MAC addresses to keep them straight.

RAID and Logical Volume Manager

RAID and LVM are supported on most recent Linux distributions and provide some key advantages. However, they can also be difficult to work with and require knowledge in particular commands to handle properly.

Redundant Array of Inexpensive Disks (RAID)

Configurations include:

RAID 0

Stripes data across for better performance. Two 160GB drives would look like a fast 320GB drive, but if you lose any one drive, you have lost everything

RAID 1

Mirrors the data across drives. Multiple copies means you have better protection, so if you lose any one drive, the rest of the system can still run. Two 160GB drives would look like a single 160GB drive. Performance is the same or slightly slower than a single drive.

RAID 5

Stripes with parity for added protection. One drive's worth is set aside for parity, so three 160GB drives would hold 320GB of data; four 160GB drives would hold 480GB of data. Since we have only two drives, this option does not apply to us. Performance is faster for read, but can be slower for writes, depending on how the parity methods are implemented.

RAID 10

Striped and Mirrored. Sometimes referred to as RAID 0+1 or RAID 1+0, this combines RAID 1 with RAID 0. Data is striped across disk 1 and disk 2, disk 3 is a mirror of disk 1 stripe, and disk 4 is mirror of disk 2 stripe. Thus four 160GB drives holds 320GB of data. If you lose any one drive, the mirrored copy is still available, so the system will be able to continue to run. Performance is same or slightly slower than a 2-drive RAID 0 configuration.

JBOD

JBOD stands for "Just a Bunch of Disks", a term meaning there is no RAID for protection or performance improvement. This refers to deployments where each disk drive is independent.

RAID-1 Considerations:

• Can mirror the entire drive ( /dev/sda <--> /dev/sdb ) or individual same-sized partitions ( /dev/sda1 <--> /dev/sdb1 )
• Can mirror swap space. This appears to be preferred best practice over just having swap space on separate disks.
• Mirrored drives appear as (/dev/md0, /dev/md1) or (/dev/dm-0, /dev/dm1)
• In general, a mirrored partition can be used wherever a native partition can be used
• Can be used as physical volumes for Logical Volume Manager

RAID rebuild: In the event a disk fails in RAID-1 mode, the single surviving drive can be used to continue operations. When a new replacement drive is available, the following procedures can be used to rebuild.

Place the surviving drive as "drive 1", remove the bad drive from the system.

• boot up
• indicate that drive 2 has failed

Place the new drive as "drive 2"

• boot up
• copy over the disk layout from "drive 1" using "sfdisk" utility
• copy over the MBR from "drive 1" using "dd" utility
• add the new partitions to /dev/md0, /dev/md1, etc. (the data will be copied over)

Logical Volume Manager (LVM2)

Logical Volume Manager allows a level of storage virtualization between the physical hardware and the operating system and applications.

Physical Volumes

A physical volume (pv) can be an entire disk drive (/dev/sda), partition (/dev/sda1), or RAID mirror (/dev/md0)

Volume Groups

A volume group (vg) combines the space capacity of one or more physical volumes. A physical volume can only be part of a single volume group. A volume group can host one or more logical volumes.

Logical Extents

The volume group is divided into fixed-size pieces called "logical extents" or LE. These are typically 32MB in size.

Logical Volume

A logical volume is a "virtual drive" that appears like a device or partition to the operating system. A logical volume can be the entire space of a single volume group, or a subset of a single volume group. Logical volumes can be increased or decreased in size, and can be moved as needed onto or away from specific physical volumes. A logical volume is one or more logical extents, so the smallest Logical Volume is one LE (typicallly 32MB). A logical extent can only be part of one logical volume.

LVM2 Considerations:

• A volume group can contain physical volumes of different sizes
• Linux cannot boot from a Logical Volume, this can be solved by having a separate /boot directory that is not part of the Logical Volume, and the rest of root (/) in the logical volume.
• Logical volumes cannot be resized using the "gparted" tool

Disk Layout

Most Linux systems only require the following:

• A Master Boot Record (MBR) that contains the boot loader and disk layout
• A root directory (/)
  • The root directory can be split up into subdirectories for /boot, /var, /home on separate partitions
• swap space (typically as big or bigger than installed RAM)

Possible Disk Layout configurations

Several disk layouts are possible. Depending on the Operating System installation procedure, you may have to install in JBOD, RAID or LVM, and then migrate to be a full RAID+LVM configuration.

1. Simple JBOD (no RAID, no LVM)

/dev/sda                                 /dev/sdb
MBR (boot loader / disk layout )         MBR (disk layout only)
  /dev/sda1 as /boot                         /dev/sdb1 for extra space
  /dev/sda5 as /
  /dev/sda6 as swap

2. RAID (no LVM)

/dev/sda                                                 /dev/sdb
MBR1 (boot loader/layout)  <-independent->                  MBR2 (boot loader/layout)
  /dev/sda1 as /boot       <- /dev/md0  ->                  /dev/sdb1
  /dev/sda5 as /           <- /dev/md1  ->                  /dev/sdb5
  /dev/sda6 as swap        <- /dev/md2  ->                  /dev/sdb6

2. LVM (no RAID)

/dev/sda                                 /dev/sdb
MBR (boot loader / disk layout )         MBR (disk layout only)                        
  /dev/sda1 as /boot                         /dev/sdb1 as physical volume
  /dev/sda5 as physical volume
where:
VolGroup00 --- combines /dev/sda5 and /dev/sdb1
LogVol00 -- as /
LogVol01 -- as swap

3. RAID (no LVM)

/dev/sda                                            /dev/sdb
MBR1 (boot loader/layout)      <-independent->      MBR2 (boot loader/layout)
  /dev/sda1 as /boot           <- /dev/md0  ->          /dev/sdb1
  /dev/sda5 as /               <- /dev/md1  ->          /dev/sdb5
  /dev/sda6 as swap            <- /dev/md2  ->          /dev/sdb6

4. RAID and LVM

/dev/sda                                            /dev/sdb
MBR1 (boot loader/layout)      <-independent->      MBR2 (boot loader/layout)
  /dev/sda1 as /boot           <- /dev/md0  ->          /dev/sdb1
  /dev/sda5 as physical vol    <- /dev/md1  ->          /dev/sdb5   
where:
VolGroup00 --- /dev/md1
LogVol00 -- as /
LogVol01 -- as swap

5. RAID and LVM with rescue partition

/dev/sda                                            /dev/sdb
MBR1 (boot loader/layout)      <-independent->      MBR2 (boot loader/layout)
  /dev/sda1 as /rescue         <- /dev/md0  ->          /dev/sdb1
  /dev/sda2 as /boot           <- /dev/md1  ->          /dev/sdb2
  /dev/sda5 as physical vol    <- /dev/md2  ->          /dev/sdb5   
where:
VolGroup00 --- /dev/md2
LogVol00 -- as /
LogVol01 -- as swap

6. RAID and LVM with rescue and scratch partitions

/dev/sda                                            /dev/sdb
MBR1 (boot loader/layout)      <-independent->      MBR2 (boot loader/layout)
  /dev/sda1 as /rescue         <- /dev/md0  ->          /dev/sdb1
  /dev/sda2 as /boot           <- /dev/md1  ->          /dev/sdb2
  /dev/sda3 as /scratch1       <-independent->          /dev/sdb3 as /scratch2
  /dev/sda5 as physical vol    <- /dev/md2  ->          /dev/sdb5   
where:
VolGroup00 --- /dev/md2
LogVol00 -- as /
LogVol01 -- as swap

Partition Sizes

The following sizes can be used:

rescue -- 4GB

This would be enough to have a basic operating system with software utilities, and include manuals, ISO images of CDs, and so on. This could fit on a single DVD or several CDs for recovery purposes.

boot -- 680 MB

This could fit on a single CD for recovery purposes. /boot will contain /boot/grub boot loader, and can contain alternative kernels to select from during the boot process. Most OS only need 100MB, so this should be plenty.

scratch -- 30GB each

This can be used to download ISO files, store "partimage" backups, and so on. These are not RAID protected, so if you lose a disk drive, these files will not be mirrored on the other drive.

base -- rest of the disk (120GB of so)

This will be the /dev/sda4 extended partition with /dev/sda5 as the extended partition as physical volume for LVM.

Creating the Disk Partition table

For some reason, with fresh disks that have no format or partition, most 32-bit LiveCD were unable to boot. To solve this, I booted a 64-bit AMD64-based LiveCD (Fedora 8 in my case), created the partitions and then could use a 32-bit LiveCD for the rest of the install. SystemRescueCD is also capable of booting in either 64-bit or 32-bit mode, use "boot: rescue64" to boot into 64-bit mode.

To save time, you can configure one drive /dev/sda then copy over the configuration to the second drive as follows:

sfdisk -d /dev/sda > sfdisk /dev/sdb

Operating System

We have decided to base this system on the XS School Server configuration. Other operating systems considered were:

Fedora 7

The XS School Server is based on Fedora 7, so if we are unable to get the XS installation kickstart file to support the disk layout, we felt a backup plan was to install Fedora 7 natively. Fedora 7 could also be used graphically by Glen on premises to help with problem determination.

Debian 4.0-r3 Etch

Ceibal (OLPC Uruguay) has chosen to use Debian 4.0-r3 Etch instead for their projects. It was a stretch goal to see if we could set up a "dual-boot" or "multi-boot" environment that would support XS-Debian, Fedora-Debian, or XS-Fedora-Debian configurations.

System Rescue

While not a complete Operating System to run EduBlog or perform development work, we might need to have an independent OS for administration or maintenance. Many utilities work best on data that is not currently active in use. This could be done with a LiveCD or as a separate partition on the disk drive.

[[ http://sysresccd.org/Main_Page | SysRescCD 1.0.3 ]] supports sshd so that with the right network setup, someone could effect software repairs remotely. It has a variety of utilities, including "partimage" that can be used to backup individual partitions or logical volumes. Installing is a matter of copying just seven files over to /sysrcd directory on a primary or mirrored partition, but not in a Logical Volume. "GRUB" as the boot loader can be updated to run this at reboot.