[TriLUG] MD & LVM Presentation

[Richard Ryder]

Hi David, (and everyone else!)

First of all I enjoyed your presentation, and my first TriLUG meeting. 
So 'thanks' to all involved!

My question was with regards the meaning of RAID0 being dirty. The md(4) 
manpage refers to just about everything except RAID0 which makes me 
think it was left off the list for a reason.

 From what I understand, arrays are marked as dirty when a write 
requires writes to multiple devices and not all writes have yet 
completed.  Is there a reason then why a RAID0 would always be dirty? 
(Other than because of the types of files stored there :P)

Hopefully soon some of my proposed purchases will be approved and I'll 
sleep a little better at night knowing that there's no more RAID0 
around.  But until then...  *sigh*

Rich

David W. Aquilina wrote:
> reetings all, 
> 
> Hope everyone enjoyed the presentation. The slides are available at http://www.trilug.org/~dwa/md-lvm-presentation. 
> 
> Regarding the question of what a 'dirty' array means, the following is from the md(4) manpage: 
> 
> 
> 
>    UNCLEAN SHUTDOWN
>        When changes are made to a RAID1, RAID4, RAID5 or RAID6 array there is
>        a  possibility  of  inconsistency  for  short  periods of time as each
>        update requires are  least  two  block  to  be  written  to  different
>        devices,  and  these  writes  probably wont happen at exactly the same
>        time.  Thus if a system with one of these arrays is  shutdown  in  the
>        middle of a write operation (e.g. due to power failure), the array may
>        not be consistent.

<snip>