[linux-lvm] Software raid on top of lvm logical volume

Luca Berra bluca at comedia.it
Thu Oct 28 06:35:31 UTC 2004

On Thu, Oct 28, 2004 at 08:01:27AM +0200, Eric Monjoin wrote:
>Theo Van Dinter a écrit :
>Well it's because we have problems in this way. We have a server 
>connected to 2 EMC Symmetrix where we assign some 70Gb and 40Gb Luns.  
>We used Powerpath to manage the dual path to the Luns and so I first 
>created mirror as this :

>But after a while I obtain that :
>Personalities : [raid1]
>read_ahead 1024 sectors
>Event: 10                 
>md9 : active raid1 [dev e9:31][1] [dev e8:e1][0]
>      42829184 blocks [2/2] [UU]
>and if we try to rebuild the mirror after after loosing access to one of 
this might be a problem with powerpath, it seems harmless tough

>the EMC, we have really bad result :
>Personalities : [raid1]
>read_ahead 1024 sectors
>Event: 26                 
>md9 : active raid1 emcpowerd1[2] [dev e8:e1][0]
>      42829184 blocks [2/1] [U_]
>      [>....................]  recovery =  1.4% (630168/42829184) 
>finish=68.1min speed=10315K/sec
this is a problem with linux md raid. it does not support fast resync
with a bitmap of changed sectors, there is a project to implement it,
but it is not yet in the standard kernel.
look on the linux-raid mailing list archives for something called 'fast
raid 1'.
i do not believe you would have any advantage in stacking md above lvm

Luca Berra -- bluca at comedia.it
        Communication Media & Services S.r.l.
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