Linux Raid - mdadm

說明

mdadm - Linux Software Raid

主要套件：mdadm
主要服務：mdmonitor (監控 Raid 狀態)

系統管理注意要項：

• 因 Linux 開機 MBR 無法作 Raid，除了初次系統安裝時，第一顆磁碟會有記錄以外，還要另外手動複寫至第二顆磁碟，同時，以後如有對第一、二顆磁碟做更換後，也需每次手動複寫開機記錄。
• /boot 磁區可以使用 raid 1
• 注意:一旦機器有磁碟故障後，切勿在沒有磁碟插入的狀況下進行系統重啟，否則在系統重啟後，既有的所有磁碟代號都會重新排序過，以至於造成管理上的困擾與磁碟設定上的錯亂。如果不小心重啟機器，不要做任何磁碟變動，只要將機器關機，然後將空的 bay 將磁碟插回機器，重新啟動機器，所有的磁碟代號應該回復之前的正常狀態。

新增 Raid

Raid 0

# mdadm --create --verbose /dev/md0 --level=0 --raid-devices=2 /dev/sdb /dev/sdc

Raid 1

# mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sdb /dev/sdc --spare-devices=/dev/sdd

Raid 5

# mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sdb /dev/sdc /dev/sdd --spare-devices=/dev/sde

使用 Raid

# mkfs.ext4 /dev/md0
# mkdir /data01
# mount /dev/md0 /data01

維護 Raid

Raid 設定檔 /etc/mdadm.conf

重新掃描 raid 與更新設定檔
mdadm --verbose --detail -scan > /etc/mdadm.conf 

設定警告郵件通知
/etc/mdadm.conf，加上這行 (NOTE: 只能設定一個信箱)

MAILADDR user@my.company.com

 顯示 Raid 整體狀態

cat /proc/mdstat

顯示 /dev/md0 詳細資訊

# mdadm --detail /dev/md0
/dev/md0:
        Version : 1.2
  Creation Time : Mon Nov  3 06:03:03 2014
     Raid Level : linear
     Array Size : 4194288 (4.00 GiB 4.29 GB)
   Raid Devices : 2
  Total Devices : 2
    Persistence : Superblock is persistent

    Update Time : Mon Nov  3 06:03:03 2014
          State : clean 
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

       Rounding : 0K

           Name : localhost.localdomain:0  (local to host localhost.localdomain)
           UUID : a50ac9f2:62646d92:725255bd:7f9d30e3
         Events : 0

    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync   /dev/sdb
       1       8       32        1      active sync   /dev/sdc

更換磁碟

1. 確認要更換的磁碟名稱與所屬的 raid，假設是 /dev/sdc, raid127
2. 執行 mdadm 從 raid127 移除磁碟 /dev/sdc
3. 取出舊磁碟，並更換新磁碟
4. 執行 fdisk 檢查新磁碟 /dev/sdc 是否存在
5. 執行 mdadm 加入磁碟 /dev/sdc 至 raid127

// 將磁碟標示為 Fail
mdadm /dev/raid127 --fail /dev/sdc

// 移除磁碟
mdadm /dev/raid127 --remove /dev/sdc

// 加入磁碟
mdadm /dev/raid127 --add /dev/sdc 

監控 Raid 狀態

/proc/mdstat

# awk '/^md/ {printf "%s: ", $1}; /blocks/ {print $NF}' </proc/mdstat
md126: [UU]
md127: [UUUUU]

# watch -t 'cat /proc/mdstat'

iotop 檢視狀態

# iotop -a -p $(sed 's, , -p ,g' <<<`pgrep "_raid|_resync|jbd2"`)

iostat 檢視狀態

# iostat -dmy 1 /dev/md127
# iostat -dmy 1 /dev/md126 

mdmonitor 警告郵件測試

# mdadm --monitor --scan --oneshot --test

警告通知的郵件內容

This is an automatically generated mail message from mdadm
running on plinux.localdomain

A Fail event had been detected on md device /dev/md/pv00.

It could be related to component device /dev/sdc1.

Faithfully yours, etc.

P.S. The /proc/mdstat file currently contains the following:

Personalities : [raid1] [raid6] [raid5] [raid4]
md126 : active raid1 sda2[0] sdb2[1]
      1049536 blocks super 1.0 [2/2] [UU]
      bitmap: 0/1 pages [0KB], 65536KB chunk

md127 : active raid6 sda3[0] sdb3[1] sdc1[2](F) sde1[4] sdd1[3]
      2809500672 blocks super 1.2 level 6, 512k chunk, algorithm 2 [5/4] [UU_UU]
      bitmap: 0/1 pages [0KB], 65536KB chunk

unused devices: <none>

移除 Raid

停止並永久移除

# mdadm --stop /dev/md0
# mdadm --remove /dev/md0

啟動 raid

# mdadm --asemble /dev/md0

NOTE : The assemble command reads the /etc/mdadm.conf file to start the array. In case you did not save your configuration in mdadm.conf before stopping the array, this command would fail. You can use the below command to recreate the mdadm.conf file :
# mdadm –examine –scan > /etc/mdadm.conf

客製系統通知程序

優點:

• 可以多個郵件收到通知信
• 通知信的內容可以客製

編輯 /etc/mdadm.conf，加上

PROGRAM /path/to/raid-event.sh

/path/to/raid-event.sh

#!/bin/bash
#
# mdadm RAID health check
#
# Events are being passed to xmessage via $1 (events) and $2 (device)
#
# Setting variables to readable values
event=$1
device=$2
# Check event and then popup a window with appropriate message based on event
if [ $event == "Fail" ];then
    message="A failure has been detected on device $device"
    else
    if [ $event == "FailSpare" ]; then
        message="A failure has been detected on spare device $device"
        else
        if [ $event == "DegradedArray" ]; then
            message="A Degraded Array has been detected on device $device"
            else
            if [ $event == "TestMessage" ]; then
                message="A Test Message has been generated on device $device"
            fi
        fi
    fi
fi

output="/tmp/my.log"
echo "event=$event" > $output
echo "device=$device" >> $output
echo $message >> $output
echo "EOF" >> $output

延伸閱讀

• http://thegeekdiary.com/redhat-cento...id-with-mdadm/
• http://xmodulo.com/create-software-r...adm-linux.html
• https://www.cyberciti.biz/faq/centos...-create-raid1/