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Re: Stuff from /bin, /sbin, /lib depending on /usr/lib libraries

Steve Langasek wrote:
> Matthew Woodcraft wrote:

>> Debian has supported booting from md RAID without using an initramfs for
>> a very long time.

> True but misleading. LILO supported it because it hard-coded the block list
> of the kernel and initrd at install time. GRUB1 never supported any RAID
> except for RAID1, as far as I'm aware. GRUB2 has supported RAID5 since
> ~2008, but has only been used as the default boot loader in Debian since
> 2011; prior to that the installer would select the best bootloader for the
> chosen disk layout - but grub2 was sufficiently experimental at that point
> that no one who actually cared about their data would be using it.

The relevant information I was supplying (to Wouter) is that there are
currently systems using md+LVM but not an initramfs.

(But I don't think what I wrote is misleading. Yes, that is how LILO
worked. Yes, I am thinking of RAID 1, as was Thomas; around here that's
an unsurprising choice for the disks holding the operating system.)

>> GRUB2 can boot from LVM or a separate /boot, but in any case
>> risk-averse people might choose to avoid root-on-LVM; this is one of
>> the reasons for putting /usr on a separate filesystem in the first
>> place.

> I wouldn't call this being risk averse, I would call it being *bad* at
> risk assessment / risk management. All the interesting data needed for
> running the system is on a filesystem other than the root filesystem
> in that case. If you actually think LVM isn't safe, you shouldn't be
> using it for /usr (and /var). If you think it is safe, you should have
> / on it as well and, if necessary, allocate a separate /boot partition
> for the bootloader.

The main risk I'm concerned about is of the system failing to boot
without tiresome manual intervention, rather than difficulties once it's
up and running.

But of course there have in the past been LVM bugs which showed up only
if the root was on LVM.

> The system I'm sending this email from would fail to boot if separate
> /usr without initramfs stops being supported.

>> Can you please elaborate on why that is?

Only because it doesn't currently use an initramfs.

If I end up having to make a choice in the near future, I imagine I'll
move /usr off LVM rather than start to use an initramfs.

I expect the time will come when I feel comfortable that for a system
running testing I can use Debian's initramfs and expect everything to
Just Work. But that time hadn't arrived the last time I got new disks,
and looking at the initramfs-tools bug page I see two open Important
bugs, each about a year old, about the md+LVM combination. So I'm not
tempted to switch in the near future.

(In contrast, for systems running stable I do use Debian's initramfs.
Though I've had boot failure due to the initramfs failing to update as
recently as the etch -> squeeze upgrades, with nothing more exotic
involved than a kernel from backports.)

Anyway, when Debian comes to decide what to do about the subject of this
thread, I suggest that the following option is worth considering:

 - a system without /usr mounted is no longer expected to be generally
   useful for 'rescue' purposes;

 - a system without /usr mounted is still expected to be capable of
   mounting a /usr filesystem held on local disks.


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