Re: RAID1, hot-swap and boot integrity

[Bill Davidsen <davidsen@tmr.com>]

Mike Accetta wrote:
> Bill Davidsen wrote:
>> Gabor Gombas wrote:
>>> On Fri, Mar 02, 2007 at 09:04:40AM -0500, Mike Accetta wrote:
>>>
>>>  
>>>> Thoughts or other suggestions anyone?
>>>>     
>>>
>>> This is a case where a very small /boot partition is still a very good
>>> idea... 50-100MB is a good choice (some initramfs generators require
>>> quite a bit of space under /boot while generating the initramfs image
>>> esp. if you use distro-provided 
>>> "contains-everything-and-the-kitchen-sink"
>>> kernels, so it is not wise to make /boot _too_ small).
>>>   
>> You are exactly right on that! Some (many) BIOS implementations will 
>> read the boot sector off the drive, and if there is no error will run 
>> the boot sector.
>>> But if you do not want /boot to be separate a moderately sized root
>>> partition is equally good. What you want to avoid is the "whole disk is
>>> a single partition/file system" kind of setup.
>>>
>>>   
>> Actually, the solution is moderately simple, install the replacement 
>> drive, create the partitions, and **don't mark the boot partition 
>> active** until the copy is complete. The BIOS will boot from the 1st 
>> active partition it finds (again, in sane cases).
>>
>> I never have anything changing in /boot in normal operation, so I 
>> admit to using dd to do a copy with the array stopped. No particular 
>> reason to think it works better than just a rebuild. After the 
>> partition is valid I set the active flag in the partition.
>>
>
> I gathered the impression somewhere, perhaps incorrectly, that the active
> flag was a function of the boot block, not the BIOS.  We use Grub in 
> the MBR
> and don't even have an active flag set in the partition table.  The 
> system
> still boots.
Now that you mention that, I have been doing the active bit thing since 
pre-grub (possibly pre-lilo) days, so it may not be effective with grub 
in the MBR. Something to add to my list of "when I'm bored and want to 
try something" list. Thanks for making the point.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979