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  #16  
Old 22nd October 2011, 04:19 AM
scott32746 Offline
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Re: Can you put /boot into software RAID during installation?

I do use software raid, but hardware you should be able to do the same.

during install you can create your first raid mirror then select /boot as the partition

I have had replace my primary boot drive by doing
moving secondary boot driving into the primary slot ,,, use grub commands to set it.
I have also booted up on the secondary drive after replacing the primary and rebuild the primary.
need to run grub commands again to have the primary drive set back.

I have set both drive up to be bootable, but not sure if it works. haven't had a drive fail yet
Your hardware / bios may play into doing something like this
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  #17  
Old 22nd October 2011, 04:30 AM
jpollard Offline
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Re: Can you put /boot into software RAID during installation?

Hardware raid presents the raid disks as a single unit to the BIOS level.

No problem at all with hardware raid.

The disks raiding configuration is part of each disk description (Normally starting with what would be the boot block if seen directly). Once the RAID definition/volume definition is set, the raid controller only presents the appearance of a disk using the rest of the disks capacity. This also makes it the responsibility of the raid controller to rebuild when a disk fails. One problem with the "fakeraid" volumes is that the controller cannot rebuild - so if a disk fails and is replaced, you can't boot because the controller cannot tell which disk is valid.

One problem with the disk drives occurs when/if they are later reused without the raid controller. The disks have a totally invalid configuration, and may refuse to work (mine refused to even partition). In my case, I could only use the disks again after I overwrote the first MB or so with 0's. Now the invalid beginning could be partitioned.
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  #18  
Old 22nd October 2011, 06:19 AM
wardhj Offline
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Re: Can you put /boot into software RAID during installation?

Quote:
Originally Posted by jpollard View Post
One problem with the "fakeraid" volumes is that the controller cannot rebuild - so if a disk fails and is replaced, you can't boot because the controller cannot tell which disk is valid.
jpollard: Thanks. I'm actually learning something.

Two questions.

The problem you describe (above) seems to be so severe that no one could sell fakeraid motherboards. Am I missing something?

My BIOS (Intel P55 chipset, fakeraid) has, of course, a page where you set the boot order [usually (a) DVD drive and (b) disk].

It has a separate page where you set the order of the two disks. Does this separate page solve the problem which you describe (above)?
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  #19  
Old 22nd October 2011, 02:04 PM
jpollard Offline
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linuxfedorafirefox
Re: Can you put /boot into software RAID during installation?

No.

The "fakeraid" controllers were aimed just like the "winmodems". Neither are true devices. In the fakeraid controller, it cannot rebuild, in the winmodems, it isn't really a modem, but a basic sound card. Modem functions are carried out in software instead of a hardware UART chip.

The fakeraid would handle base reads from a disk volume. If one of the disks failed (and was replaced) it can not rebuild - it depends on the host system to do that. One of the first things done in the rebuild software on windows is to copy the boot blocks. If the system is rebooted, the fakeraid would not know which drive is really valid. It can/should boot when the bad disk is removed, as there is no ambiguity in what to read from. Once the system is booted, and then the replacement drive plugged in, the software could/should be able to identify and rebuild the RAID. But that depends on being able to hotplug the disks in, and have the OS able to add the new disk to the system.

Up until recently (last couple of years) hotplugging of hard disks didn't really work. USB, no problem. ESATA I believe is handled the same way.
SATA... no. It has to be plugged in when the SATA controller is scanned, and rescanning I understand, can cause I/O failures on other drives.

I don't know if the current linux drivers used with the Fakeraid know how to rescan without causing problems.
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  #20  
Old 23rd October 2011, 03:21 AM
wardhj Offline
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Re: Can you put /boot into software RAID during installation?

Quote:
Originally Posted by jpollard View Post
One of the first things done in the rebuild software on windows is to copy the boot blocks. If the system is rebooted, the fakeraid would not know which drive is really valid.
jpollard: Thanks. This agrees with my experiments (Intel P55 chipset). I've seen the computer boot from the replacement disk and bring up an old installation of Fedora.

I would suggest that the BIOS do these two things:

(a) store the serial numbers of the RAID drives in non-volatile memory, and

(b) on reboot use the stored serial numbers to determine which drive is valid and which drive is the replacement.

Then the problem you describe (quoted above) would not exist.
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  #21  
Old 23rd October 2011, 01:01 PM
jpollard Offline
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linuxfedorafirefox
Re: Can you put /boot into software RAID during installation?

Unfortunately, it can't... unless you can count on the fakeraid controller to have a bios that can.

The problem is if you have to replace the fakeraid controller you have lost everything.

What the bios really needs is for the fakeraid to have an extension that allows you to define the raid so that you designate what is considered the primary drive in the configuration. Then, during boot, in any ambiguous situation the primary drive is favored. That way it won't matter which drive failed, you are able to direct it to use the valid drive as the boot drive.
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  #22  
Old 24th October 2011, 08:10 AM
leigh123linux
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Re: Can you put /boot into software RAID during installation?

Threads merged.
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  #23  
Old 12th November 2011, 05:48 PM
jenaniston Offline
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Re: Can you put /boot into software RAID during installation?

Quote:
Originally Posted by wardhj View Post
jpollard: Thanks. I'm actually learning something.
. . .
Yep me too . . .

My problem / confusion / grasp of this (and some attempt at help)
was with the difference(s) between hardware and software RAID.
The Fedora installation guide at least helped me clarify that software RAID can use - if not outright requires - a /boot partition

Great post/thread and merge !
(and now I can experiment with this in F16 even).
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  #24  
Old 6th August 2012, 01:36 PM
laughingakio Offline
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Re: Can you put /boot into software RAID during installation?

You know the reason for all this madness is that Fedora hasn't synced with upstream grub 2 just yet. Fedora 18 anaconda is supposed to do this. I did this in Arch and you can do it on grub2 Deb distros. Part of Red Hats fork of grub stinking up the process. Thank the powers that its targeted.
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  #25  
Old 6th August 2012, 02:44 PM
jpollard Offline
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Re: Can you put /boot into software RAID during installation?

Not really....

How does grub get loaded? The MBR/EFI loads from given blocks. Software raiding will not validate a volume until grub2 can build a volume. So grub2 can't build a volume until it gets loaded into memory....

Even if the /boot filesystem is properly raided, the blocks on the mirror volume do not have to match that of the first disk.

Boot blocks are not part of the filesystem - so the boot block on the first volume of a raid (the MBR) get lost if the first volume is removed - they were not copied to the second volume, and even if they get copied, nothing says they will be valid for the second volume. And again, you can't boot.

Now some part of the EFI (bios equivalent) might be able to build a raid volume... but it has to be in flash first.
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  #26  
Old 6th August 2012, 03:35 PM
laughingakio Offline
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Thumbs up Re: Can you put /boot into software RAID during installation?

What do you mean not really? Grub gets loaded because one of the drives successfully booted. Grub2 is smart enough to know which drive to boot if one is unbootable. You don't need /boot anymore. That limitation is because the anaconda installer is using the Red Hat fork all the way up until Fedora 18. I'm not sure if they even have gotten that far yet. I guess you could check the status but I'm not bothering until a release.

I don't know what you want I guess. I know how to set up a boot failure safe raid1 from two disks without a boot partition. You can't do that unless you get away from that fork.

I repeat, step away from the fork!
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  #27  
Old 6th August 2012, 04:01 PM
jpollard Offline
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linuxfirefox
Re: Can you put /boot into software RAID during installation?

From what drive does it load?

Since the primary boot (bios or UEFI) doesn't know about raids grub2 can't get loaded.

grub2 also needs extended data - and the location of that extended data is not necessarily in the same blocks on the alternate.

The only way to do it is to put grub on every drive in the system.

That said, if the two drives are physically identical, and both contain the partitions with /boot, THEN copying the boot blocks between them SHOULD work. But it is not necessarily true.
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  #28  
Old 6th August 2012, 06:08 PM
DBelton Offline
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Re: Can you put /boot into software RAID during installation?

?? Fedora doesn't fork grub2 anymore. They forked legacy grub and maintained it for years after upstream stopped, but Fedora it pretty much running the upstream grub2. They have renamed a few of the files, but that's about it.

Also, Fedora (and grub2) has been able to boot from a software RAID (DMRAID or MDRAID) since F16. You possibly might have to manually add the insmod statements for raid, mdraid09, and mdraid1x, though.

To get software RAID /boot to work from anaconda:
You can install the appropriate grub2 modules manually from anaconda's console before rebooting from the installer, or from rescue mode.
Code:
Edit the file /mnt/sysimage/boot/grub2/grub.cfg and add the lines:

insmod part_msdos
insmod raid
insmod mdraid09
insmod mdraid1x

Now run these commands:

chroot /mnt/sysimage
grub2-install --modules="part_msdos raid mdraid09 mdraid1x" /dev/sda
grub2-install --modules="part_msdos raid mdraid09 mdraid1x" /dev/sdb
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  #29  
Old 6th August 2012, 06:51 PM
laughingakio Offline
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Talking Re: Can you put /boot into software RAID during installation?

@DBelton, thank you very much. I have been looking for that magic.
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  #30  
Old 6th August 2012, 08:39 PM
jpollard Offline
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linuxfirefox
Re: Can you put /boot into software RAID during installation?

The important piece is having to run grub2-install once for each disk.
The blocks (and any block maps included) written are not updated and are specific to each drive.

You have to do that for every update to grub.
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