in-situ conversion to FT disk config?

[Bill McGonigle]

On Nov 15, 2005, at 08:36, Michael ODonnell wrote:

> theoretically it should be
> possible to lay the {RAID,LVM,otherFT} metadata down on the disks
> such that any existing {MBR,filesystem} bits remain untouched
> and the disk becomes usable as part of an FT config

I bet this has something to do with the MS-DOS-style disk layout Linux 
x86 uses.  There just isn't extra space to add the proper headers, I'm 
guessing.

I've done what you're asking for on Solaris and Mac OS X before, so 
it's definitely do-able, but those probably had some forethought for 
RAID or at least extra-fields when they were designed.  On Solaris 
there was a nice GUI so I don't know how it actually worked (drag and 
drop RAID is fun), but on Mac OS X the theory is:  Mark partition A as 
a degraded RAID member, create a RAID set with it as the only member, 
add in the blank disk, and then the kernel gets to synchronizing.  I'm 
not sure if you can do that on a boot volume or not.

With modern Linux RAID (post raidtab) there's some place on disk where 
the RAID descriptors are stored but I'm not sure where they put it or 
what they store there.

The happy news is distros like FC4 create everything as LVM by default 
- so in a few years we can fondly "remember when you had to.." about 
this.  With the price and near silence of new disk drives I'm taking to 
calling people stupid for not at least mirroring.

Now then, when you're going to copy your filesystem to the new RAID 
member, don't forget to get all the special files:

   http://blog.bfccomputing.com/index.php?p=25


-Bill
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