[linux-lvm] Drive gone bad, now what?

[Gert van der Knokke]

John Stoffel wrote:

>Gert> I didn't expect lvm to restore the missing data, I guessed it
>Gert> would just let me access the rest of the data.
>
>At this point, you have to think, how can my filesystem cope with the
>loss of a 60gb chunk of data in the middle (start or end even) of the
>300+ gb of data?  There's all sorts of meta-data and true data which
>is now gone, and re-building the filesystem into a consistent state is
>really impossible.  
>
Hmm, and so I think LVM still needs a warning label :-)

I wonder why LVM doesn't work the other way around:
Create filesystems on several disks and then concatenate these to the 
outside as one large filesystem. This way if one drive goes bad you can 
always individually mount the drives and use the data.

>If you are looking for a large/cheap/reliable bunch of storage,
>instead of mirroring, you might want to think about RAID5 instead.
>
No, what we're looking for is an 'expandable as needed' filesystem and 
this is what LVM pretends to be.
Our server acts as a NAS and when it gets full you add more drives or 
exchange them for (a set of) larger ones.
To the user it still is the same network share, just bigger.

>your case, you had a mix of disks, so what you could do is build a
>pair of RAID5 arrays using disks of the same size for each array
>(minimum of three disks each of course) and then stripe the filesystem
>across both arrays.  
>
>To add more storage, you need to work on chunks of three disks, but
>since 120gb disks are going for around $100 these days, it's not that
>expensive.
>
We will look into raid5, but considering the hardware limitations 
(number of onboard ports and such), for step by step upgrades the 2 disk 
mirror option is best I think.

Gert