auto-read-only question

auto-read-only question

[Albert Pauw]

  Can anybody explain to me what "active (auto-read-only)" mean in 
/proc/mdstats? So the full entry in /proc/mdstats is:

Personalities : [raid1]
md2 : active (auto-read-only) raid1 sdd[1] sde[0]
           1015808 blocks super external:/md127/0 [2/2] [UU]

md1 : active (auto-read-only) raid1 sdb[1] sdc[0]
           1015808 blocks super external:/md127/0 [2/2] [UU]

md127 : inactive sdb[4](S) sdf[3](S) sde[2](S) sdd[1](S) sdc[0](S)
            163840 blocks super external:ddf

unused devices: <none>


(Yes, two raid1 sets in a ddf container).

Thanks,

Albert

Re: auto-read-only question

[Robin Hill]

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On Fri Feb 25, 2011 at 05:07:48PM +0100, Albert Pauw wrote:

>   Can anybody explain to me what "active (auto-read-only)" mean in 
> /proc/mdstats?
> 
When the array is assembled, it's set in "auto-read-only" mode. As soon
as anything tries to write to it, it gets set to normal write mode (or
you can trigger this manually by doing "mdadm -w" on the array). I'm not
sure why this is done - possibly it make it simpler for md to skip
running various internal processes on that array (as it knows that the
array isn't being dirtied).

I usually see this with swap arrays - most filesystems will immediately
open the array in read/write mode, so trigger the switch.

Cheers,
    Robin
-- 
     ___        
    ( ' }     |       Robin Hill        <robin@robinhill.me.uk> |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |

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