raid10 on centos 5

I am trying to set up raid 10 and so far with no luck. I have 4 drives, and Anaconda will not let me do raid 10. mdadm doesn't have the raid 10 personality loaded. When I create the array manually like so:

2 drives in /dev/md11 as raid1
2 drives in /dev/md12 as raid1
md11 and md12 in /dev/md10 as raid0

Everything looks fine from the shell, but anaconda only sees md11 and md12.

The only choice I see is to set up LVM over md11 and md12. Is this really raid10?

Russ

No LVM over the two RAID 1's is more like RAID 1c which is just a concatenation of RAID 1's. You don't get the striping that you get in RAID 10.

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Ruslan Sivak
Sent: Friday, May 04, 2007 11:22 AM
To: [email protected]
Subject: raid10 on centos 5

I am trying to set up raid 10 and so far with no luck. I have 4 drives,

and Anaconda will not let me do raid 10. mdadm doesn't have the raid 10

personality loaded. When I create the array manually like so:

2 drives in /dev/md11 as raid1
2 drives in /dev/md12 as raid1
md11 and md12 in /dev/md10 as raid0

Everything looks fine from the shell, but anaconda only sees md11 and md12.

The only choice I see is to set up LVM over md11 and md12. Is this really raid10?

Russ

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That's what I guessed. Can anyone let me know if it's possible to set up a real md raid10? Do I need to custom compile the kernel and do a kickstart install or something?

Russ

cat /proc/mdstat

is the raid10 personality installed?

No, it's not. How would I go about installing it?

Personalities: [raid0] [raid1] [raid6] [raid5] [raid4]

Russ

Compile into the kernel, boot new kernel then create your RAID 10 volume with mdadm :)

So a custom kernel is needed? Is there a way to do a kickstart install with the new kernel? Or better yet, put it on the install cd?

Russ

Unsure for CentOS, I use Debian and always compile my own kernel.

Justin.

have you tried:
modprobe raid10

?

David

Yes, no such luck.

Russ

} -----Original Message-----
} From: [email protected] [mailto:linux-raid-
} [email protected]] On Behalf Of Ruslan Sivak
} Sent: Friday, May 04, 2007 12:22 PM
} To: [email protected]
} Subject: raid10 on centos 5
}
} I am trying to set up raid 10 and so far with no luck. I have 4 drives, } and Anaconda will not let me do raid 10. mdadm doesn't have the raid 10 } personality loaded. When I create the array manually like so:
}
} 2 drives in /dev/md11 as raid1
} 2 drives in /dev/md12 as raid1
} md11 and md12 in /dev/md10 as raid0
}
} Everything looks fine from the shell, but anaconda only sees md11 and } md12.
}
} The only choice I see is to set up LVM over md11 and md12. Is this } really raid10?
}
} Russ

You are making a RAID1+RAID0 array.
Try making a real RAID10 array with 4 drives. This way you would only have 1 array with 4 drives.

From the mdadm man page:
Currently, Linux supports LINEAR md devices, RAID0 (striping), RAID1
(mirroring), RAID4, RAID5, RAID6, RAID10, MULTIPATH, and FAULTY.

Notice RAID10 is listed, use that. Man mdadm for more info.

However, I would (and do) use RAID6. With RAID6 any 2 disks can fail without data loss. With RAID1+RAID0, any one disk can fail, a second failure has a 1 in 3 chance of vast data loss.

I hope this helps,
Guy

Guy,

That's what I've been trying to do. Unfortunatelly, my distro, CentOS 5 (based on RHEL 5, I believe), does not have the RAID10 personality in the kernel. I guess I would have to compile my own kernel and load the module through a driver disk. Would that work? Are there some instructions somewhere I can follow?

Russ

You shouldn't need to build a new kernel, just extract the SRPM for the initial install (CentOS 5, no updated kernels), use the config for the appropriate kernel (SMP, UP, i386/x86_64), enable the raid10 module and do a 'make modules'. You may need to do a minor amount of tweaking in the installer image to include this, but nothing serious. Alternately, just building a driver disk with the module and source it in the install. Interesting that it's not enabled in the installer image, because it's present in a fully-booted system... space limitations?

/eli

It is not present in a fully booted system for me either. Are you running centos 5?

How would I make a driver disk? I'm not very familiar with this.

Russ

} -----Original Message-----
} From: Ruslan Sivak [mailto:[email protected]]
} Sent: Friday, May 04, 2007 7:22 PM
} To: Guy Watkins
} Cc: [email protected]
} Subject: Re: raid10 on centos 5
}
} Guy Watkins wrote:
} > } -----Original Message-----
} > } From: [email protected] [mailto:linux-raid- } > } [email protected]] On Behalf Of Ruslan Sivak
} > } Sent: Friday, May 04, 2007 12:22 PM
} > } To: [email protected]
} > } Subject: raid10 on centos 5
} > }
} > } I am trying to set up raid 10 and so far with no luck. I have 4 } drives,
} > } and Anaconda will not let me do raid 10. mdadm doesn't have the raid } 10
} > } personality loaded. When I create the array manually like so:
} > }
} > } 2 drives in /dev/md11 as raid1
} > } 2 drives in /dev/md12 as raid1
} > } md11 and md12 in /dev/md10 as raid0
} > }
} > } Everything looks fine from the shell, but anaconda only sees md11 and } > } md12.
} > }
} > } The only choice I see is to set up LVM over md11 and md12. Is this } > } really raid10?
} > }
} > } Russ
} >
} > You are making a RAID1+RAID0 array.
} > Try making a real RAID10 array with 4 drives. This way you would only } have
} > 1 array with 4 drives.
} >
} > >From the mdadm man page:
} > Currently, Linux supports LINEAR md devices, RAID0 (striping), RAID1
} > (mirroring), RAID4, RAID5, RAID6, RAID10, MULTIPATH, and FAULTY.
} >
} > Notice RAID10 is listed, use that. Man mdadm for more info. } >
} > However, I would (and do) use RAID6. With RAID6 any 2 disks can fail } > without data loss. With RAID1+RAID0, any one disk can fail, a second } > failure has a 1 in 3 chance of vast data loss.
} >
} > I hope this helps,
} > Guy
} >
} > -
} >
}
}
} Guy,
}
} That's what I've been trying to do. Unfortunatelly, my distro, CentOS 5 } (based on RHEL 5, I believe), does not have the RAID10 personality in } the kernel. I guess I would have to compile my own kernel and load the } module through a driver disk. Would that work? Are there some } instructions somewhere I can follow?
}
} Russ

I don't know how to make a driver disk. Also not much on making modules. From what I know, linux only loads the RAID modules it needs. My system does not have raid0 or raid10 loaded. But both loaded when I used modprobe. I have FC6, upgraded from FC5 using yum, so maybe not 100% FC6.

Anyway, you were not making a RAID10 array. You were making 2 RAID1 arrays and then 1 RAID0 array. That does not need the RAID10 module (AFAIK).

If I recall, there is an issue of nesting arrays like you were doing. The problem was related to auto starting them. But I don't recall any details, and maybe it has been corrected.

Guy