raid-one

[Les]

Hi, Karl,
	The very first thing you should mention is backing up the disk.  Always
a good idea, but especially so when formatting or partitioning disks.
One mistake can spoil your whole day.

Regards,
Les H
On Wed, 2007-08-15 at 14:34 -0600, Karl Larsen wrote:
>     I decided to write another paper that covers setting up a raid-1 
> computer :-)   As always it is a lot of work. Here is the start of it. 
> Please find errors and such and bring them to my attention. The paper is 
> about 1/3 complete.
> 
> 
>     A raid-1 configuration is defined as two Hard Drives (HD) having the 
> same computer software on each of them. If one HD fails the other will 
> continue to run and the computer will operate as if nothing had happened.
> 
>     Most of what is here is from an email of Jeffrey Ross who is a 
> member of the Fedora Users List. I have just used some examples and 
> re-ordering to suit my way of thinking.
> 
>     There are some special raid configuration software. One is "fdisk" 
> and with that you can make partitions that have the special fd 
> configuration. The other is called "mdadm" and it is written to be just 
> a raid technical assett. Read man mdadm to see how capable it is.
> 
>     Here is what you MUST do.
> 
> 1. Your current HD and F7 partition is /dev/sda5 and your new HD will be 
> /dev/hdbx where x is a number from 1 to 7. The first thing to do is 
> decide how to lay out the many partitions it can look like this:
> 
> /dev/sdb1 = /boot
> /dev/sdb2 = /usr
> /dev/sdb3 = swap
> /dev/sdb4 = extended partition
> /dev/sdb5 = /var
> /dev/sdb6 = /
> /dev/sdb7 = /home
> 
>     The partition size you find out by using "du -ch". For example to 
> see how big /usr must be in a Terminal cd /usr and there type $ du -ch. 
> On my F7 /usr is 3.4 Gbytes. So /dev/sdb2 should be 4 Gbytes or larger.
> 
>     Make the partitions with "fdisk". To do this you need to open a root 
> Terminal and use # fdisk /dev/sdb. If your /dev/sdb is a new HD it will 
> not show any partitions when you say p. On my old HD it shows this:
> 
> Command (m for help): p
> 
> Disk /dev/sdb: 160.0 GB, 160041885696 bytes
> 255 heads, 63 sectors/track, 19457 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
> 
>    Device Boot      Start         End      Blocks   Id  System
> /dev/sdb1   *           1        1217     9775521   83  Linux
> /dev/sdb2            1218        1945     5847660   83  Linux
> /dev/sdb3            1946        1961      128520   82  Linux swap / Solaris
> /dev/sdb4            1962       18534   133122622+   5  Extended
> /dev/sdb5            1962        7060    40957686   83  Linux
> /dev/sdb6            7061       12159    40957686   83  Linux
> /dev/sdb7           12160       18534    51207156   83  Linux
> 
> Command (m for help):
> 
> As you can see the HD has 160 GB and it has 5 Linux file systems and a 
> swap partition and /dev/sdb4 is an Extended partition.
> 
>     For our raid-1 work we want all partitions to be Linux raid 
> autodetect which you get with "fdisk" when you make a new partition. 
> Here is how it is done:
> 
> Command (m for help): n
> First cylinder (12160-18534, default 12160):
> Using default value 12160
> Last cylinder or +size or +sizeM or +sizeK (12160-18534, default 18534): 
> 16000
> 
> Notice that I choose 16000 to end the partition. If you look the new 
> partition has 30 GB total space.
> 
> /dev/sdb7           12160       16000    30852801   83  Linux
> 
> The type of partition is wrong. We don't want Linux. We want raid and 
> that is done this way:
> 
> Command (m for help): t
> Partition number (1-7): 7
> Hex code (type L to list codes): l
> Hex code (type L to list codes): fd
> Changed system type of partition 7 to fd (Linux raid autodetect)
> 
> Command (m for help): p
> 
> Disk /dev/sdb: 160.0 GB, 160041885696 bytes
> 255 heads, 63 sectors/track, 19457 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
> 
>    Device Boot      Start         End      Blocks   Id  System
> /dev/sdb1   *           1        1217     9775521   83  Linux
> /dev/sdb2            1218        1945     5847660   83  Linux
> /dev/sdb3            1946        1961      128520   82  Linux swap / Solaris
> /dev/sdb4            1962       18534   133122622+   5  Extended
> /dev/sdb5            1962        7060    40957686   83  Linux
> /dev/sdb6            7061       12159    40957686   83  Linux
> /dev/sdb7           12160       16000    30852801   fd  Linux raid 
> autodetect
> 
> Command (m for help):
> 
> To save what we have shown here type w as in write the new things. I 
> used q which means quit without saving.
> 
>     In our example we have to do the same thing for /dev/sdb1 through 7 
> and it is easy to do and will not take long. Now our new HD is set to be 
> a raid-1 HD.
> 
> 2.
> Now back to the old HD. We need to make the raid partition numbers which 
> to make life simple will be the same as the new HD. We do this with 
> "mdadm" as follows:
> 
> mdadm --create /dev/md1 --level=1 --raid-devices=2 /dev/sdb1 missing
> mdadm --create /dev/md2 --level=1 --raid-devices=2 /dev/sdb2 missing
> mdadm --create /dev/md3 --level=1 --raid-devices=2 /dev/sdb3 missing
> mdadm --create /dev/md5 --level=1 --raid-devices=2 /dev/sdb5 missing
> mdadm --create /dev/md6 --level=1 --raid-devices=2 /dev/sdb6 missing
> mdadm --create /dev/md7 --level=1 --raid-devices=2 /dev/sdb7 missing
> 
> 
> -- 
> 
> 	Karl F. Larsen, AKA K5DI
> 	Linux User
> 	#450462   http://counter.li.org.
>