Why do I get a DegradedArray event with mdadm

Posted by azera on Server Fault See other posts from Server Fault or by azera
Published on 2010-03-10T12:59:04Z Indexed on 2010/03/29 5:43 UTC
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Hello

Just so we're clear on what's happening:

  • I bought 4 new sata 2 drives, with the intent of using them in a raid5
  • all drive are fully recognised by both my bios and my linux box (gentoo)
  • I created a raid5 array, fiddled a bit with it to understand how it works, how to monitor ect
  • At some point, this triggered a degradedarray event, even though the array is brand new. I tried to stopping the array and recreating a new array with the same drive but the new array starts degraded too.

here is what I used to create it

mdadm --create -l5 -n4 /dev/md/md0-r5 /dev/sdb /dev/sdd /dev/sde /dev/sdf

here are the output from my /proc/mdstat and mdadm --detail --scan

**mdstat**

Personalities : [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md127 : active raid5 sdf[4] sde[2] sdd[1] sdb[0]
      4395415488 blocks level 5, 64k chunk, algorithm 2 [4/3] [UUU_]
      [>....................]  recovery =  2.8% (41689732/1465138496) finish=890.3min speed=26645K/sec

unused devices: <none>

**detail**

ARRAY /dev/md/md0-r5 metadata=0.90 spares=1 UUID=453e2833:81f22a74:64188b84:66721085

As such I have a couple questions:

  • does a raid5 array always start in degraded mode at first ?
  • why does sdf have the number 4 between bracket instead of 3, why does it see a spare disk and why is the 4th drive marked with _ instead of U ? (bad configuration ?)
  • How can I recreate the array from scratch, do i have to format each drive on its own before recreating it ?

Thanks for any help, I'm not sure about what I should do at the moment

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