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Linux RAID Setup

Posted on 2013-05-29
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Last Modified: 2013-06-02
I've found some rather nifty instructions on setting up softRAID on linux (https://raid.wiki.kernel.org/index.php/RAID_setup). But I can't discern whether the boot device is/can/or should be part of the raid. I presume I will download, install and configure mdadm while running a normal /dev/sdx device. Should the boot device be a physically separate drive? Can the RAID be set up on top of and incorporate the boot device? Has anyone done this?
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Question by:jmarkfoley
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Assisted Solution

by:Jan Springer
Jan Springer earned 150 total points
ID: 39204843
I recommend at least mirroring the boot drive.  What I don't do is include the boot partition in LVM or do RAID with /proc.
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David earned 350 total points
ID: 39204947
Build 2 partitions on all disk drives.  

(sda0,sdb0,sdc0,sdd0.   Do sda0 & sda1 as a RAID1 for the O/S,  mirror sdc0 & sdd0 for swap.
Then sd[a-d]1 for a RAID6.  Mount as /data and put all your data there.

Yes, boot device can and should be mirrored.  In another thread I just said to make it a 4-way RAID1 just so everything is same size, but that is overkill and you can use 2 disks for a mirrored swap.
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Author Comment

by:jmarkfoley
ID: 39205005
dlethe - I'm going to try this in about an hour. I'll keep you posted. Thanks for your feedback. I'm sure I'll have more questions.
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Author Comment

by:jmarkfoley
ID: 39209796
I'm moving steadily forward following the instructions at https://raid.wiki.kernel.org/index.php/RAID_setup. I'm deferring doing the boot drive for the moment (one thing at a time!). I've create the RAID array as:

mdadm --create /dev/md0 --metadata 1.2 --verbose --level=6 --raid-devices=4 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1

This took 21 hours! Is that normal or do I just have a pathetically slow system? These are 2TB drives.

I then made the file system as:

mke2fs -v -m .1 -b 4096 -E stride=128,stripe-width=384 /dev/md0

which went rather quickly -- 10 minutes-ish. Then, I started the RAID:

mdadm --assemble --scan --uuid=39edeb69:297e340f:0e3f4469:81f51a6c

 Despite the abundant information in that link, it really doesn't tell me what do do next. Just mount the file system? I made that assumption and did:

mount /dev/md0 /mnt/RAID

is that sufficient? I'm going to assume it is and start copying data to the drive. I expect that will take a very long time, so if someone can reply as to what my next step should be in the meantime, I'd apprecate it. That way, I can blow off the copying and do whatever should be done.

THX
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by:jmarkfoley
ID: 39209841
Problem ... I don't seem to have the right settings in /etc/fstab. In fstab I have

/dev/md0        /mnt/RAID       ext2        defaults,uid=99  1   1

but when I try to mount it I get:

mount: wrong fs type, bad option, bad superblock on /dev/md0,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

I can mount w/o the uid=99, but I need to have the folder owned by 99 (nobody) to samba mount it. This may not be a RAID specific question, but any ideas? I'm stuck not being able to copy data to the RAID.
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Author Comment

by:jmarkfoley
ID: 39209883
duh! never mind on that last permissions question. I simple had to change the permissions on the mountpoint itself! So, please refer back to posting ID: 39209796.

Mainly, I'd like to know if there is something else I need to do for this RAID to function properly other than simply mounting it.
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Author Comment

by:jmarkfoley
ID: 39214728
This question seems to have grown stale as I've posted 4 comments with no reply; probably because I've wandered from the original question about using RAID for the boot device. So, I'm going to close this one out and refer interested experts to a new link I've posted specifically addressing my last comment in this question: http://www.experts-exchange.com/OS/Linux/Q_28145407.html

As to the original boot/RAID issue, I've done more research. There is an extensive discussion of this at https://raid.wiki.kernel.org/index.php/Tweaking,_tuning_and_troubleshooting#Making_the_system_boot_on_RAID. This seems quite a bit more complex that dlethe's response in ID: 39204947, above. I'm going to experiment with this on a computer lab rat before attempting to configure this on a production machine.

I have an ASUS P8Z77-V LK motherboard that advertised RAID support on the box, but after reading the user guide it appear that I have to create a Windows driver onto a floppy disk to support this. Since I have neither Windows nor a floppy drive, this is not an option (it seems to me that it should be rather simple to create a RAID-1 with an on-board SATA controller, but what do I know).

Therefore, for the time being, I've resorted to my old standby, a "latent" mirror. I.e., once a day (or so) I copy everything from the main drive to an offline backup drive -- even properly lilo'ing the backup drive. Once a month, I wipe the backup drive with mkfs and start fresh. This works fine except that, in case of main drive failiure,  I have to manually swap the drives (or cables) to boot off the backup, and I'll lose whatever files were created/modified since the most recent "mirror" backup unless they were backed up elsewhere.

End of saga ... for now.
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Author Closing Comment

by:jmarkfoley
ID: 39214730
Thanks for the comments
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