[gentoo-user] Creating RAID devices - udev question

[gentoo-user] Creating RAID devices - udev question

[Brian Parish]

I am trying to add a software RAID 5 disk set to an existing machine installed 
using genkernel.  All the RAID support is compiled into the kernel, but 
no /dev/md? device files exist.  I can create these using mknod and make the 
RAID, but they don't survive a reboot.  How do I tell udev to create these 
files as persistant devices?

TIA
Brian
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Re: [gentoo-user] Creating RAID devices - udev question

[Richard Fish]

On 11/12/05, Brian Parish <bmp@univexsystems.com> wrote:
> I am trying to add a software RAID 5 disk set to an existing machine installed
> using genkernel.  All the RAID support is compiled into the kernel, but
> no /dev/md? device files exist.  I can create these using mknod and make the
> RAID, but they don't survive a reboot.  How do I tell udev to create these
> files as persistant devices?

udev doesn't handle software raid devices.  You need to edit
/etc/conf.d/rc, and make sure that "raid" appears in RC_VOLUME_ORDER. 
You will also need to edit/create /etc/mdadm.conf to describe your
raid array.  Gentoo will then take care of creating the raid devices
as part of the system startup.

-Richard

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Re: [gentoo-user] Creating RAID devices - udev question

[Mike Williams]

On Sunday 13 November 2005 01:49, Brian Parish wrote:
> I am trying to add a software RAID 5 disk set to an existing machine
> installed using genkernel.  All the RAID support is compiled into the
> kernel, but no /dev/md? device files exist.  I can create these using mknod
> and make the RAID, but they don't survive a reboot.  How do I tell udev to
> create these files as persistant devices?

All partitions in the RAID set need to be set to partition type fd (Linux raid 
autodetect), then the kernel will build the arrays during startup.

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Mike Williams

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Re: [gentoo-user] Creating RAID devices - udev question

[Richard Fish]

On 11/12/05, Mike Williams <mike@gaima.co.uk> wrote:
> On Sunday 13 November 2005 01:49, Brian Parish wrote:
> > I am trying to add a software RAID 5 disk set to an existing machine
> > installed using genkernel. All the RAID support is compiled into the
> > kernel, but no /dev/md? device files exist. I can create these using mknod
> > and make the RAID, but they don't survive a reboot. How do I tell udev to
> > create these files as persistant devices?
>
> All partitions in the RAID set need to be set to partition type fd (Linux raid
> autodetect), then the kernel will build the arrays during startup.

FYI, this is only true if the raid drivers are compiled into the
kernel (no modules), and you do _not_ use an initramfs to boot the
system.  If you use an initramfs, the kernel skips the autodetection
of raid arrays.

-Richard

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Re: [gentoo-user] Creating RAID devices - udev question

[Brian Parish]

On Sunday 13 November 2005 17:23, Richard Fish wrote:
> On 11/12/05, Mike Williams <mike@gaima.co.uk> wrote:
> > On Sunday 13 November 2005 01:49, Brian Parish wrote:
> > > I am trying to add a software RAID 5 disk set to an existing machine
> > > installed using genkernel. All the RAID support is compiled into the
> > > kernel, but no /dev/md? device files exist. I can create these using
> > > mknod and make the RAID, but they don't survive a reboot. How do I tell
> > > udev to create these files as persistant devices?
> >
> > All partitions in the RAID set need to be set to partition type fd (Linux
> > raid autodetect), then the kernel will build the arrays during startup.
>
> FYI, this is only true if the raid drivers are compiled into the
> kernel (no modules), and you do _not_ use an initramfs to boot the
> system.  If you use an initramfs, the kernel skips the autodetection
> of raid arrays.
>
> -Richard

I did and it does (skip that is).  Thanks again Richard.

Brian
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Re: [gentoo-user] Creating RAID devices - udev question

[Brian Parish]

On Sunday 13 November 2005 17:33, Brian Parish wrote:
> On Sunday 13 November 2005 17:23, Richard Fish wrote:
> > On 11/12/05, Mike Williams <mike@gaima.co.uk> wrote:
> > > On Sunday 13 November 2005 01:49, Brian Parish wrote:
> > > > I am trying to add a software RAID 5 disk set to an existing machine
> > > > installed using genkernel. All the RAID support is compiled into the
> > > > kernel, but no /dev/md? device files exist. I can create these using
> > > > mknod and make the RAID, but they don't survive a reboot. How do I
> > > > tell udev to create these files as persistant devices?
> > >
> > > All partitions in the RAID set need to be set to partition type fd
> > > (Linux raid autodetect), then the kernel will build the arrays during
> > > startup.
> >
> > FYI, this is only true if the raid drivers are compiled into the
> > kernel (no modules), and you do _not_ use an initramfs to boot the
> > system.  If you use an initramfs, the kernel skips the autodetection
> > of raid arrays.
> >
> > -Richard
>
> I did and it does (skip that is).  Thanks again Richard.
>
> Brian
Removing the initramfs seemed like the line of least resistance here, so being 
basically lazy, that's what I did.  /dev/md0 is now created and I can create 
my RAID array happily enough.

This still doesn't survive a reboot though.  i.e. I have to run the mdadm 
--create command again.  I assumed that this required something in 
mdadm.conf, so I updated that with all the magic numbers shown by mdadm -D.  
No change though.  Is this an rc-update issue, or something?

Thanks yet again
Brian
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Re: [gentoo-user] Creating RAID devices - udev question

[Brian Parish]

On Saturday 19 November 2005 16:19, Brian Parish wrote:
> On Sunday 13 November 2005 17:33, Brian Parish wrote:
> > On Sunday 13 November 2005 17:23, Richard Fish wrote:
> > > On 11/12/05, Mike Williams <mike@gaima.co.uk> wrote:
> > > > On Sunday 13 November 2005 01:49, Brian Parish wrote:
> > > > > I am trying to add a software RAID 5 disk set to an existing
> > > > > machine installed using genkernel. All the RAID support is compiled
> > > > > into the kernel, but no /dev/md? device files exist. I can create
> > > > > these using mknod and make the RAID, but they don't survive a
> > > > > reboot. How do I tell udev to create these files as persistant
> > > > > devices?
> > > >
> > > > All partitions in the RAID set need to be set to partition type fd
> > > > (Linux raid autodetect), then the kernel will build the arrays during
> > > > startup.
> > >
> > > FYI, this is only true if the raid drivers are compiled into the
> > > kernel (no modules), and you do _not_ use an initramfs to boot the
> > > system.  If you use an initramfs, the kernel skips the autodetection
> > > of raid arrays.
> > >
> > > -Richard
> >
> > I did and it does (skip that is).  Thanks again Richard.
> >
> > Brian
>
> Removing the initramfs seemed like the line of least resistance here, so
> being basically lazy, that's what I did.  /dev/md0 is now created and I can
> create my RAID array happily enough.
>
> This still doesn't survive a reboot though.  i.e. I have to run the mdadm
> --create command again.  I assumed that this required something in
> mdadm.conf, so I updated that with all the magic numbers shown by mdadm -D.
> No change though.  Is this an rc-update issue, or something?
>
More info on this:  It turns out that the main problem is/was that at the time 
the system is attempting to mount the RAID set, not only has it not been 
assembled, but the devices which compose it do not exist.  /dev/sda, b and c 
are being created sometime later in the boot process.

I have now implemented a smooth work-around by:

1. Setting the RAID in fstab to noauto and no checking
2. Creating a script in /etc/init.d which assembles and mounts the RAID set
3. Adding this script to the default group using rc-update

While this means that everything works nicely, it does seem like a kludge and 
there is presumably a way to have the SATA (SCSI) devices created early in 
the boot process, so that the RAID set can be assembled and ready for the 
entry in fstab to be processed.

cheers
Brian
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Re: [gentoo-user] Creating RAID devices - udev question

[Mike Williams]

On Saturday 19 November 2005 14:15, Brian Parish wrote:
> > This still doesn't survive a reboot though.  i.e. I have to run the mdadm
> > --create command again.  I assumed that this required something in
> > mdadm.conf, so I updated that with all the magic numbers shown by mdadm
> > -D. No change though.  Is this an rc-update issue, or something?
>
> More info on this:  It turns out that the main problem is/was that at the
> time the system is attempting to mount the RAID set, not only has it not
> been assembled, but the devices which compose it do not exist.  /dev/sda, b
> and c are being created sometime later in the boot process.

That's certainly interesting. What SATA card do you have?
If it's got in kernel drivers, having them compiled into the kernel will get 
them setup before raid starts.

-- 
Mike Williams

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Re: [gentoo-user] Creating RAID devices - udev question

[A. Khattri]

On Sun, 20 Nov 2005, Brian Parish wrote:

> I have now implemented a smooth work-around by:
>
> 1. Setting the RAID in fstab to noauto and no checking
> 2. Creating a script in /etc/init.d which assembles and mounts the RAID set
> 3. Adding this script to the default group using rc-update

Yes, this seems like an unnecessary kludge to me.

I have several servers all using software RAID, udev and 2.6 kernels (all
are SCSI, one is SATA) without any problems.



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Re: [gentoo-user] Creating RAID devices - udev question

[Neil Bothwick]

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On Sat, 19 Nov 2005 16:19:53 +1100, Brian Parish wrote:

> Removing the initramfs seemed like the line of least resistance here,
> so being basically lazy, that's what I did.  /dev/md0 is now created
> and I can create my RAID array happily enough.
> 
> This still doesn't survive a reboot though.  i.e. I have to run the
> mdadm --create command again.

Are the partitions comprising the RAID marked 'Linux raid autodetect' in
cfdisk/fdisk?


-- 
Neil Bothwick

Scrute the inscrutable; eff the ineffable.

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