Re: LINEAR RAID, little help

Hi,

On Sat, 07 Apr 2007, Rich wrote:

Er, I went with Linear as reading around people seemed to recommend this 
for odd sized drives (my old drives are 80's, 120 and 320's) also a read 
somewhere that data on the other drives is more recoverable that most of 
the other RAID's.

You just want to make a large filesystem out of odd sized disks.  I guess
that's fair enough.  The only reservation I'd have is that with N disks
your likelihood of failure is multiplied by N as any disk failure takes the
array down.  Personally, I'd be more inclined to try and put a separate
filesystem on each disk and use symlinks to pull them together into one
tree.

But now I know why linear raid can be more useful than raid-0, thanks.

Well it contains stuff like TV and films a lot of which my friends have, 
so loosing it is not that big of a deal just inconvenient. As I said 
before I read linear was a better choice for odd sized drives and had 
better data recovery that the other RAID's

I guess you're using it similarly to LVM then. 

http://en.wikipedia.org/wiki/Logical_Volume_Manager_(Linux)
http://tldp.org/HOWTO/LVM-HOWTO/

It sounds reasonable that recovery would be more feasible than RAID-0 but
neither would be nice to have to do.  RAID1, 5, etc. would be less likely
to require recovery as they have redundancy so a single disk failure
shouldn't take down the array at all.

I'm sure I read somewhere on the mdadm page in one of the posts about 
adding support for linear growing, and that was dated 2004 so it might 
be in there? Just wasn't to sure how to do it...

This looks like your page.

http://cgi.cse.unsw.edu.au/~neilb/SoftRaid

and the mdadm changelog has it:

Changes Prior to 1.7.0 release
   -   Support "--grow --add" to add a device to a linear array, if the
       kernel supports it.  Not documented yet.

I've only grown raid5 arrays myself.  I imagine you must do --add to add
the extra disk partition to the array and then do "mdadm --grow
--size=max", same as with raid5.  

Gavin