Adding new disks, include in volume group

[Jonathan Rawle]

Scot L. Harris wrote:

> BTW: how much of a problem is it with multiple drive file systems when
> one of those drives fails?  Assumption here is that no raid is being
> used for that volume.
> 
> And is a chance of such a failure a multiple of the drives in the
> volume?  Or is it higher?
> 

Assuming all drives have the same probability of failure, the overall
probability of a drive failing scales linearly with the number of drives in
the system.

If you use LVM with linear mapping mode, the chance of losing a particular
file if a drive fails should be the same as it would be using the same
number of drives without LVM. (OK, it might be slightly different as the
odd file will span multiple physical volumes, but this has a negligible
effect on the overall statistics unless you have lots of very large files
and many small physical volumes!)

However, if you use striped mapping (which is presumably NOT the default in
Fedora), failure of any drive will result in the loss of all your files. In
this case the probability of loss scales with the number of drives.


I'm not expert when it comes to LVM, but I recently read a few docs and
people seem to suggest that a RAID/LVM combination isn't always a good idea
as the two are not aware of each other so don't make allowances for the way
the other works. Not sure if this is out of date advice though.

Jonathan