Add disk to my RAID5 array

  • Hi guys,


    I have an OpenMediaVault NAS configured with 4 WD Red 4TB in a RAID5 array.
    I want to add 2 new disks to this array and unfortunately I cannot find how to do it.
    I physically installed the disks in the server and start the NAS.
    I click on Grow button in the RAID management tab but my disks were shown in spare in the details (below the details with one added disk, I decided to unplug the other one to perform the extension with one disk at a time...).
    I have read several posts and it seems that a command line can solve this issue (mdadm --grow...) but I don't know where to enter this command.
    If I connect a screen and a keyboard to my server I have a login line but if I enter my login and pswd the page actualize and ask me again login and pswd.
    I am a complete beginner in NAS and Linux in general so I hope that someone can help me :)


    Thank you in advance!


    Version : 1.2
    Creation Time : Fri Dec 9 01:30:37 2016
    Raid Level : raid5
    Array Size : 8790405120 (8383.18 GiB 9001.37 GB)
    Used Dev Size : 2930135040 (2794.39 GiB 3000.46 GB)
    Raid Devices : 4
    Total Devices : 5
    Persistence : Superblock is persistent


    Intent Bitmap : Internal


    Update Time : Sun Aug 27 01:12:16 2017
    State : clean
    Active Devices : 4
    Working Devices : 5
    Failed Devices : 0
    Spare Devices : 1


    Layout : left-symmetric
    Chunk Size : 512K


    Name : NASnicoOMV:Cube2 (local to host NASnicoOMV)
    UUID : f8b8f2fc:ef76fb8d:d603eeee:ca66164c
    Events : 10022


    Number Major Minor RaidDevice State
    0 8 0 0 active sync /dev/sda
    1 8 16 1 active sync /dev/sdb
    2 8 32 2 active sync /dev/sdc
    3 8 48 3 active sync /dev/sdd


    4 8 64 - spare /dev/sde

    • Offizieller Beitrag

    If I connect a screen and a keyboard to my server I have a login line but if I enter my login and pswd the page actualize and ask me again login and pswd.

    The above is somewhat puzzling. If you're logging in with a KB and monitor, are you logging in as (user) root, with the password you set when you installed OMV? If you try to log in as (user) admin and password on the console (KB and Monitor), the screen will reset endlessly. (In OMV ver's 3.x)


    You can log into OMV, without using a keyboard and monitor, by using Putty. You can find putty here. -> Putty (At some point, you'd need it in any case.)


    After Putty is installed on a Windows PC, connect to the IP address of OMV, on port 22 (SSH). On the login screen, login as root with the password set at installation.


    ________________________________________________________



    I want to add 2 new disks to this array and unfortunately I cannot find how to do it.
    I physically installed the disks in the server and start the NAS.
    I click on Grow button in the RAID management tab but my disks were shown in spare in the details (below the details with one added disk, I decided to unplug the other one to perform the extension with one disk at a time...).
    I have read several posts and it seems that a command line can solve this issue (mdadm --grow...) but I don't know where to enter this command.


    FIRST WARNING!!
    The last time someone on the forum tried to reshape their array (add a spare disk to the array and enlarge it), their array crashed. Read about it here. -> Bad Outcome
    There are many reasons why arrays fail:
    - In some cases they fail when recovering from a disk failure. In the case above, a reshape (adding a disk into the array) seemed to cause a fatal failure in one of the other disks in the array.
    - Recoveries and reshapes are a hard drive torture test for every drive in the array.
    - (For the reasons mentioned above) Mixing drives of significantly different ages - NOT a good idea.
    - Even if it's only half full, you have a large array. A reshape is going to take awhile which, again, is hard on all hard drives.
    - There are plenty of reasons why arrays fail, that have no explanation. It's the nature of the beast.



    SECOND WARNING!!
    If you do not have a full backup of the data in your array and / or, you can't afford to lose the array for any reason, leave it alone.
    ________________________________________________________


    You've said that you're new to Linux.
    My advice to you would be, on one of your Desktop PC's with 8 GB RAM, install Virtual Box. Then create an OMV virtual machine. With 5 or even 10, 5GB virtual hard disks, you could test RAID scenarios and, in other cases, you could run tests on OMV, experiment with plugin's, etc., without consequence. There's a lot to be learned and this is a safe way to do it.


    Second; with 2 new 4TB disks, you're close to being able to have real backup (a 2nd copy of your data) using Rsync and other proven and reliable methods. The purpose and intent behind RAID is not for backup. RAID was created for the 24X7 enterprise computing world, for data "availability", back when hard drives were smaller. As disks grow larger, the benefits that RAID provide rapidly diminish. In any case, if you're looking to keep your data safe, RAID is not the way to do it.
    ________________________________________________________


    Based on the information you provided, the command line to add a disk to the array is:
    (*First, verify in the GUI, under RAID Management that the device name of your array is /dev/md0. If it's not, modify the following accordingly.*)


    mdadm --grow /dev/md0 --raid-devices=5


    After entering the above, depending of the CPU and other factors, the NAS may get sluggish. Given the size of your disks, the reshape will take a long time. (A day or more is not outside the realm of possibility.) Also, during that period, the WEB GUI may become unresponsive. My suggest would be to leave it alone and, do not turn off the NAS.
    ________________________________________________________


    As you've been told by tinh-x7 this is at your own risk. Further, if you're not familiar and comfortable on the command line, again, the above is not a good idea. Given that you're new to Linux, if the reshape fails, it probably wouldn't be realistic or productive to attempt an array recovery. It might be best to rebuild it from scratch or, better yet, take another approach and truly protect your data.

  • Thank you very much for the responses!
    It seems that I need to have a deep thinking on what I need and what I want... and to meditate on the difference between RAID and backup.
    This is a good opportunity to do it!


    Indeed I used the admin login, I will try with root one.


    The main reason to add the two new disks is that my NAS is now full ;(
    When I created the NAS last year I wanted to test the OMV solution (free solution, large community of users) because I had reached limitations with my Synology NAS and I decided to start with 3 disks (budget).
    I chose WD Red 3TB, same reference for the 6 disks.
    I use it mainly for media center purpose (Plex Media Server) and for some data storage (personal videos for example).
    I understand now that this is not the best option for the second one, and I will think about finding a way to secure these data on an alternative solution. I will save the important data on something else.


    Concerning adding disks to the RAID array, if I remember well I did it once last year to add the fourth disk and it worked perfectly.
    I must have used an option in the OMV software.
    I don't understand why it is not easily feasible this time.


    I think I cannot restart from scratch without losing all my media center data because I have no other disk capacity to welcome these 9TB data.
    I will update the post when I am ready to progress on this.


    Thank you again for helping!
    Have a nice Sunday.

    • Offizieller Beitrag

    I put a bit of strength in those warnings because of the potential outcomes. There are some who have used RAID for years, expanded their array, recovered from failures multiple times, etc., etc., without problems. On the other hand, those without backup who have had a fatal array failure,, they tend to be "ex-RAID" users. (Experience can be a tough, mixed martial arts style, teacher.)


    The vast majority of users really don't understand what RAID is. I've had far more than average exposure to RAID arrays, from former employment, and you know my opinion. (If you use it fine, but solid backup is essential.) There are others on this forum who supported RAID platforms for a living. Their opinions are as strong, or even stronger than my own.


    This is the eventuality you must recognize and plan for:
    If you continue to use the same PC and RAID array, just as it is with a single disk - whether it's tomorrow or 5 years from now - your array is going to fail. You must plan for that failure or lose everything.
    ____________________________


    My priority is not performance (I have two users), and it's not 24x7 availability (while I can recovery rapidly, it might take 15 to 30 minutes), my wife can wait. My priority is data preservation which is why I spread my disks over different PC's and "backup". (Note, good backup doesn't have to be expensive.)


    It depends on what you're looking for. In your case, if it's disk pooling, (adding two or more disks to a single mount point, creating a single virtual disk), there are ways to pool disks without using RAID. (LVM, UnionFS, etc.)


    From appearances you have much more than the average amount of data, that's typical of a home NAS. Maybe it's time to evaluate what you have that's irreplaceable and back that up. (Rsync to an internal or external drive?) As for the rest of your data, without backup, it's a matter of time and a roll of the dice.


    BTW: When it comes to platforms (OMV versus other offerings out there), the questions of "availability", "performance", "data preservation", etc., are the same. These questions are solved by your approach, not the platform.
    I started off using Windows Home Server. I did a lot of searching, and testing of potential candidates using virtual machines. OMV, with a couple plugin's that customize it for what I want to do, is actually better and far more stable, than WHS.


    If you find something better, please share your findings.


    Good Luck

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