On Dec 1 2007 06:19, Justin Piszcz wrote:
> RAID1, 0.90.03 superblocks (in order to be compatible with LILO, if
> you use 1.x superblocks with LILO you can't boot)
Says who? (Don't use LILO ;-)
>, and then:
>
> /dev/sda1+sdb1 <-> /dev/md0 <-> swap
> /dev/sda2+sdb2 <-> /dev/md1 <-> /boot (ext3)
> /dev/sda3+sdb3 <-> /dev/md2 <-> / (xfs)
>
> All works fine, no issues...
>
> Quick question though, I turned off the machine, disconnected /dev/sda
> from the machine, boot from /dev/sdb, no problems, shows as degraded
> RAID1. Turn the machine off. Re-attach the first drive. When I boot
> my first partition either re-synced by itself or it was not degraded,
> was is this?
If md0 was not touched (written to) after you disconnected sda, it also
should not be in a degraded state.
> So two questions:
>
> 1) If it rebuilt by itself, how come it only rebuilt /dev/md0?
So md1/md2 was NOT rebuilt?
> 2) If it did not rebuild, is it because the kernel knows it does not
> need to re-calculate parity etc for swap?
Kernel does not know what's inside an md usually. And it should not
try to be smart.
> I had to:
>
> mdadm /dev/md1 -a /dev/sda2
> and
> mdadm /dev/md2 -a /dev/sda3
>
> To rebuild the /boot and /, which worked fine, I am just curious
> though why it works like this, I figured it would be all or nothing.
Devices are not automatically readded. Who knows, maybe you inserted a
different disk into sda which you don't want to be overwritten.
> More info:
>
> Not using ANY initramfs/initrd images, everything is compiled into 1
> kernel image (makes things MUCH simpler and the expected device layout
> etc is always the same, unlike initrd/etc).
>
My expected device layout is also always the same, _with_ initrd. Why?
Simply because mdadm.conf is copied to the initrd, and mdadm will
use your defined order.
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