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Old 03-02-2011, 03:04 PM   #1
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Registered: Mar 2011
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Trying to introduce new hdd into mdadm RAID5, having problems (Debian)

I wasn't sure if this qualifies as a newbie question or not, but I figured since it seems simple enough that I would post it here.

About a month ago I cobbled up a server from an old computer and HDD. Feeling ambitious, I decided to spend a little cash on a set of 3 1TB hdds when they went on sale. With some help from a friend (who I don't think is a member of these boards), I was able to get Debian up and running as well as Samba and was also able to access my share over the home network. (Amazingly this is from having almost little knowledge of the command line and *nix distros in general).

Yesterday I added a fourth hard drive that wasn't part of the raid array to the set, and while at first it didn't recognize the new hdd (it does now), it made note that one of the drives from my raid array had been completely removed, yet in POST all four drives show up.

Below is the detail for md0 in mdadm:
        Version : 1.2
  Creation Time : Wed Feb  2 00:55:33 2011
     Raid Level : raid5
     Array Size : 1953518592 (1863.02 GiB 2000.40 GB)
  Used Dev Size : 976759296 (931.51 GiB 1000.20 GB)
   Raid Devices : 3
  Total Devices : 2
    Persistence : Superblock is persistent

    Update Time : Wed Mar  2 01:39:32 2011
          State : clean, degraded
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 512K

           Name : sas:0  (local to host sas)
           UUID : 67504025:838a3320:19da5a54:fad2ec4f
         Events : 124

    Number   Major   Minor   RaidDevice State
       0       8       17        0      active sync   /dev/sdb1
       1       0        0        1      removed
       2       8       65        2      active sync   /dev/sde1
And here are a list of drives/partitions that show up when I "ls /dev/sd*"

/dev/sda   /dev/sda2  /dev/sdb   /dev/sdc   /dev/sdd  /dev/sde1
/dev/sda1  /dev/sda5  /dev/sdb1  /dev/sdc1  /dev/sde
Now I know that the syntax for adding a new drive into a raid array via mdadm is "mdadm --add /dev/md1 /dev/sdd1", but that renders itself useless if I can't have all four drives in the RAID5 array.

So I guess after all of this my question is: where did my second drive in the RAID array go and how do I get it back? (Before anyone figures it's a bad drive I did a SMART test on all drives yesterday and they are all fine).
Old 03-02-2011, 03:42 PM   #2
Registered: Jul 2003
Location: Los Angeles
Distribution: RedHat8 2.4.18-14 RedHat9 2.4.20-8 FreeBSD 5.2.1 Ubuntu 10_4 Mandrake 2.4.21-0.13mdk
Posts: 118

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I did something in the past, but not to that size. I had 3 drives, the first was the OS, the extra 2 drives were used as swap files for a proxy.

In any case, if the extra drive is showing signs of failure, it will not mount correctly. But, if you managed to get it to work, then it has to be specified in fstab or mtab. I just do not recall if that is the correct way to mention to your linux distro where the extra drives are.


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