[lug] LVM and disk failure

[Daniel Webb]

On Sun, Jan 08, 2006 at 02:09:41PM -0800, Jeffrey Siegal wrote:

> You don't really need LVM for this at all.  You can just split up  
> your user accounts across multiple physical devices (or RAID sets).   
> Of course, LVM adds some value in that you can more easily move user  
> accounts around if need be, including during normal operations.
 
I thought about that, and that may still be the way I go.  LVM would be nice
because you don't have to worry about figuring out which partition has enough
space, assigning a user to the right partition, etc.

> If you do use LVM this way, note that there is no guarantee that a LV  
> won't be spread across multiple PVs (not just two), if that's where  
> the space is available when its created.  You can assign LVs to  
> specific PVs within a volume, but it takes extra effort.

So to get the nice convenience of not worrying about which PV I'm using, I
lose a lot of the robustness.  I'll have to look into that, I wonder how smart
it is about that?  Suppose there are a bunch of 5GB holes in the VG and 100GB
of empty space at the end of the VG.  I want to create a new 30GB LV, and I
would like it to go preferentially in that end space so it isn't smeared over
many disks.  But if I have to figure out how to do that manually, I might as
well just be doing the direct solution above.

Looking at the man pages, I see that LVM2 has "allocation policy" and
"contiguous" is an option.  Unfortunately, the version I have has a note at
the bottom saying basically that contiguous doesn't work.

So anyone have experience with evms?