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Re: [PLUG] how to put partitions on RAID?
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On Tue, Mar 18, 2003 at 08:46:39AM -0800, Wayne Dawson wrote:
> I don't know precisely what a "superblock" is, but it seems to be data
> stored on the disk that relates to its participation in a raid. I believe
> this is created when I use mdadm to create an array.
I have both mdadm and raidtools installed. as long as you mdadm -C you
should be creating superblocks. -B doesn't if my memmory serves me
correctly.
> >here is my mounted partitions
> >/dev/md1 on / type reiserfs (rw,errors=remount-ro)
> >/dev/md0 on /boot type ext2 (rw,errors=remount-ro)
>
> Where should I put the commands to assemble my /dev/md* devices so that
> they can be seen and/or mounted at boot time?
I don't know about grub but i know lilo can understand the superblocks and
boot up from the raid partitions. Once it starts booting It behaves just
like any other install. it will mount the filesystems you have in
/etc/fstab.
> Ok, a couple of comments here. You only have three partitions, instead of
> the five or so most people set up for Linux. Any particular reason for
> this? Does it have anything to do with using raid?
I'm only working with 9gb of space also. I don't want to lock myself into a
partition scheme that i might grow out of. One one system I administered,
the number of users increase to the point on a few of my boxes that var got
filled out. I think the partition scheme is a matter of personal taste.
> Also, you have your /boot on your raid. I had to recompile my kernel to
> get it to see my scsi devices and to handle software raid - that is, to
> have these capabilities built into the kernel, instead of being loaded via
> modules. How does the boot process work so that the computer boots from a
> software raid (scsi) device? I've been told that this can't be done.
Well I boot from raid. I don't even have the modules compiled into the
kernel. I just made sure my initrd.img had everything i needed in it.
> My best guess is that really you can boot from the /boot partition on
> either of the 2 scsi devices (sda1 or sdb1, in my case), but not the /boot
> partition of the assembled md1 device, since the kernel (and other stuff?)
> has to be loaded before the md1 device can even *be* assembled.
Booting from raid is possible nowdays. one of the reasons for the
superblock for the raid(if i understand things correctly).
> Once my system is booted and md1 assembled, I can make changes to /boot and
> reboot from either one, as before. But by having md1 (/boot) assembled as
> a raid, I can keep the two /boot partitions in sync.
Don't boot from the seperate partitions anymore.
> All of this will work, of course, only if my system is capable of booting
> from a scsi device. But I believe it is not a limitation of Linux that
> will prevent this setup from working.
I'm booting directly from the raid1 partition. You just need to read more
man pages.(still not sure about grub support for raid booting, You might
want to read up on that or just switch to lilo) If you don't want to
compile in the scsi and raid drivers, You will need to read up on making a
initrd.img with everything you need inside it. I mostly work on debian
systems,so I'll only be able to help you out with the general linux issues.
To satisfy my curiosity, Why are you playing with raid stuff?
Laters,
N-Tropy
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