Maxime Boissonneault wrote:

Robin Hill a écrit :

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On Mon May 25, 2009 at 01:05:15PM -0400, Maxime Boissonneault wrote:

 

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Hello,
I am using Ubuntu Hardy with 3x500GB drives and the following RAID
configuration :

/boot is on a 100MB RAID1
/ is on a 30GB RAID0
/home is on a 906GB RAID5

    

Ouch - why RAID0 for /?  If you lose a single drive then all the
configuration, etc. is down the drain.  I'd suggest rethinking this
while you're going through the rebuild process anyway.

  

That is why I do backups of / on /home regularily. I first did a RAID0 
for performance. I did some testing on performance of RAID0,1,5 and 
RAID1 was pretty lousy (I put the results of my tests here : 
http://cqed.physique.usherbrooke.ca/~mboisson/htpc.php?sec=raid_test )
I guess I should have used a RAID5, but RAID1 seems like a terrible 
idea considering the really bad performances.

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I want to replace the 3 drives by 3 1TB drives.

Here is how I planned to do it :
0- Backup my /home on some external disk.
1- backup / with something like :
sudo tar cvpzf /backup.tgz --exclude=/media --exclude=/proc
--exclude=/lost+found --exclude=/backup.tgz --exclude=/mnt 
--exclude=/sys
--exclude=/home /
mv /backup.tgz $1
    

You'll need to do the tar in single user mode (init 1) to ensure there's
no open files when you're backing up (or use a bootable CD).

  

I used this backup before to restore the system and it seemed to work 
pretty well.

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2- Replace 1 disk
3- Boot and let the RAID1 and RAID5 reconstruct
    

You'll have to boot to a CD then - your root FS is trashed at this
point.

 

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4- Replace 1 other disk
5- Boot and let the RAID1 and RAID5 reconstruct again
6- Replace the last disk
7- Boot and let the RAID1 and RAID5 reconstruct one last time
8- Boot and restore the backup on the RAID0 / partition.
9- Resize the /home partition to 1 TB.

I suspect there will be a problem replacing the primary disk, but I 
guessed
that I could solve this simply by changing which is the primary disk 
in the
BIOS.

Is there any other problem that will or could happen ?

    

See above - your current plan is pretty much doomed I'm afraid.

 

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For example, I am not sure if the raid manager is on the /boot 
partition or
on the /. I guess if it is on /, it won't work at all since the raid 
manager
itself won't be able to run ?
Also, is it possible to boot and access a command line to restore 
the backup
with a failed / partition ?

I am also unsure about how I should proceed to resize the /home 
partition.
Is this done through mdadm ?

    

No, you'll have to delete & recreate the partition using fdisk.

 

quoted

Please enlight me on any problems that I will have.

    

An easier option (assuming you want to keep the arrays as currently
setup) would be to boot from a CD and do a full copy of each of the
500GB disks to the 1TB disks.  You'll then just need to resize the
last partition (assuming /home is set up on the last partition on the
disks anyway) and grow the array and filesystem.

A _better_ option (if possible) would be to install all the drives in
the system concurrently, then you can boot from CD and create arrays on
the new drives and copy the data across.  You'll also need to update
mdadm.conf (and the initrd if you're using one) to indicate the new
array IDs.

HTH,
    Robin
  

I can not install more drives in the computer. It is a home theater 
computer in a small case. I was expecting to be able to let the raid 
manage the copies itself.

If the / was on a RAID5, would it be able to boot with 2 disks ?
If so, is it possible to convert my RAID0 to a RAID5 ?
For example, I could boot on a CD, backup / onto /home, delete the 
RAID0 array and recreate it as RAID5, then restore the backup. Would 
this work ?

Based on my testing (somewhat old now) and regular use, I would say 
raid10 is probably your best bet. It's fast and secure, and with the -f2 
option for "far" copies it's able to give high transfer rates.

-- 
bill davidsen [off-list ref]
  CTO TMR Associates, Inc

"You are disgraced professional losers. And by the way, give us our money back."
    - Representative Earl Pomeroy,  Democrat of North Dakota
on the A.I.G. executives who were paid bonuses  after a federal bailout.



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