raid-check: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/sbin/raid-check - from package: mdadm

You may install the required package with command yum install {package}

Error in other languages:
raid-check: bevel nie gevind nie
raid-check: comandă negăsită
raid-check: comando não encontrado
raid-check: commande introuvable
raid-check: command not found
raid-check: käsku ei ole
raid-check: không tìm thấy lệnh
raid-check: komanda nerasta
raid-check: Kommando nicht gefunden.
raid-check: kommandot finns inte
raid-check: komut yok
raid-check: nie znaleziono polecenia
raid-check: níor aimsíodh an t-ordú
raid-check: no se encontró la orden
raid-check: no s'ha trobat l'ordre
raid-check: opdracht niet gevonden
raid-check: parancs nem található
raid-check: perintah tidak ditemukan
raid-check: príkaz nenájdený
raid-check: příkaz nenalezen
raid-check: команда не найдена
raid-check: командата не е открита
raid-check: 命令找不到
raid-check: コマンドが見つかりません