Re: RAID1, hot-swap and boot integrity

[Mike Accetta <maccetta@laurelnetworks.com>]

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.
-- 
Mike Accetta

ECI Telecom Ltd.
Data Networking Division (previously Laurel Networks)