Re: What do Events actually mean?

Neil Brown wrote:

On Saturday March 22, jpiszcz@lucidpixels.com wrote:

quoted

On Sat, 22 Mar 2008, Peter Rabbitson wrote:

quoted

Robin Hill wrote:

quoted

On Fri Mar 21, 2008 at 07:01:43PM -0400, Bill Davidsen wrote:

quoted

Peter Rabbitson wrote:

          UUID : b6a11a74:8b069a29:6e26228f:2ab99bd0 (local to host Arzamas)
        Events : 0.183270

As you can see it is pretty old, and does not have many events to speak of.

What do the 'Events' actually represent and what do they mean for RAID0,
RAID1, RAID5 etc?

An 'event' is one of:
   switch from 'active' to 'clean'
   switch from 'clean' to 'active'
   device fails
   device is added
   spare replaces a failed device after a rebuild

I think that it all.

None of these are meaningful for RAID0, so the 'events' counter on
RAID0 should be stable.

Unfortunately, the number looks like a decimal but isn't.
It is a 64bit number.  We print out the top 32 bits, then the bottom
32 bits.  I don't remember why.  Maybe I'll 'fix' it.

quoted

How are they calculated?

   events = events + 1;


Feel free to merge this text into the wiki.

Thanks Neil :)

http://linux-raid.osdl.org/index.php?title=Event

I also added:

== What are they for? ==
When an array is assembled, all the disks should have the same number of events.
If they don't then something odd happened.

eg:
If one drive fails then the remaining drives have their event counter
incremented. When the array is re-assembled the failed drive has a different
event count and is not included in the assembly.


This lead me to ponder: How/when are events reset to equality?
I wrote:
  The event count on a drive is set to zero on creation and reset to the
majority on a resync or a forced assembly.

Is that right?

David