i just enlarged the sda and sdb partitions underneath /boot, which broke
their raid1 association, and then learned at grub rescue that the
centos7/grub2 mbr indeed looks for the raid device, not just an underlying
partition, so i wonder if sda were dead if perhaps it might still just
work, if all i do is tell the bios to boot sdb.

On Thu, Jan 11, 2018 at 8:10 PM, Nathan O'Brennan <plugaz at codezilla.xyz>

> I did try this in Centos 7. My sda failed and I had to do some messing to
> get it to boot as degraded, however it was possible. If I remember
> correctly I had to switch sata cables so sdb looked like sda and I had just
> happened to manually install the boot onto both mbrs.  In the end I put a
> third drive in just for the OS and boot so I could keep my raid volumes
> completely separated.
> In a pinch you can also boot using Kali or something similar and manually
> mount the degraded array if you need to pull data off.
> On 2018-01-11 16:07, gregrwm wrote:
> my setup is sda and sdb are partitioned identically, boot is raid1/ext3,
> swap is raid1, root is raid1/lvm/ext4, each raid1 has a partition on sda
> and a partition on sdb.
> if sda goes south, will centos7 still boot?  it won't work unless the sdb
> mbr points to the sdb member of /boot, which means the sdb mbr would not be
> an exact copy of the sda mbr.
> i kind of expect it to be more simpleminded and less friendly such that it
> will only work if sda is removed and sdb becomes addressable as sda.
> or perhaps the mbr is smarter than i expect and looks for a UUID, in which
> case it would work either way.
> has anyone actually tried this in centos7?
this concludes test 42 of big bang inflation dynamics.  in the advent of an
actual universe, further instructions will be provided.
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