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Old 05-30-2003, 07:11 PM   #1
Registered: Mar 2003
Location: Massachusetts, USA
Distribution: RH 8, Solaris, Windoze eXPunged
Posts: 520

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RAID, probably a dumb question, but I need help

Hi all,

I am thinking of setting up a RH 8 server and I am debating using RAID 1 with 2 Seagate SCSI disks. Now, I know nothing about RAID on a linux system. Basically, I will have the 2 HDD's on a SCSI controller, but I guess my question is:

Do I need this SCSI card to be a RAID card also, or can I set up software RAID in linux (on installation). Will this work ok? Will whatever partitions I set up and all data be copied (mirrored) to the other drive so if the primary drive fails, I can simply runn off of the second drive without missing a beat? I have been reading a little about RAID on linux, but I would really like some help. Thanks a million!


Or would it just be easier to buy a SCSI card that is a hardware RAID card? I know they cost a lot more, but money is not really a concern.

Last edited by WorldBuilder; 05-30-2003 at 07:20 PM.
Old 05-30-2003, 08:54 PM   #2
Registered: Feb 2003
Posts: 482

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yes you can go the software way. i just did it and when i boot into the second drive i can't even tell, the only way that i know is that the test is larger on the boot scripts. it's pretty cool.

i'm not that familiar with scsi, so don't quote me. for eide, you want to have the drives set up on seperate ribbons so that if one fails the other drive won't be toast also. i don't know if you would want to do this with your scsi, but i would probably go that way if it were mine.

here's a tip.

cfdisk -P /dev/hda > partitions
cfdisk -P /dev/hdc < partitions

that will print out a partition list of your drive to a file and then have that file make the new partitions on the second. that way you know that they are identical.

good luck.
Old 05-31-2003, 06:02 PM   #3
Registered: Aug 2002
Location: Cape Town, South Africa
Distribution: Red Hat 8.0 (Home), Red Hat 8.0 (Work)
Posts: 388

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linux software raid is great, you don't need a HW controller, try it with the sw raid first and see if you can afford a (minor) performance hit.

the advice emetib gave about the partitions is good, just make sure that your first hd is partitioned as you want it to be. If you are planning on RAID 1 I would just create 1 partition per disk (i have obtained best results with ext3 for RAID1).

you don't have to put devices on different ribbons, that would be silly on sCSI as each device is independent. The only way that they will both fail at the same time is if the cable itself fails, or if the controler fails.

Any other questions post here and we'll iron it out.
Old 05-31-2003, 11:27 PM   #4
Registered: Mar 2003
Location: Massachusetts, USA
Distribution: RH 8, Solaris, Windoze eXPunged
Posts: 520

Original Poster
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I guess that's what is confusing to me. Perhaps it's the terminology. For instance:

I setup 2 HDD's.
I install RH 8, setting up, let's say:
5GB /
5GB /var
100MB /boot
1 GB swap
1 GB /etc
Remaing space /home

I set up all that on the first HDD, and then when the system boots for the first time, I set up a RAID 1 system. So, the entire setup of the first HD gets copied bit by bit to the second physical drive? If the first drive fails, I just boot off the second? Please elaborate, and thanks for the help so far!!!!!

Old 06-02-2003, 10:12 PM   #5
Registered: Feb 2003
Posts: 482

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basically yes.

the reason that i set up my hd's on seperate controllers (ribbons) is so that if one does fail then your ok with the other. if both of your drives are on the same controller, and that fails then what was the purpose of having it mirrored? that's what i was saying.

for if your drive fails and you want to boot of the mirror, then drop in your boot disk/cd and tell it where to boot from-

linux root=/dev/hd??

the first ? is what drive and the second ? would be what partiiton.

you should be able to set up your raid on your install, mdk gave me an option on the install. don't know if rh does or not. so yes, set up your partition table and then go into the raid configuration after your reboot. the how-to's on raid are both easy to follow and confusing at the same time. i would read then though so that you have an idea on what to do to get it going. if you have any questions after that we'll be happy to help.



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