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    Configure Software RAID 1 in Centos

    IT Discussion
    linux centos centos 6 rhel rhel 6
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    • scottalanmillerS
      scottalanmiller @Lakshmana
      last edited by

      @Lakshmana said:

      When I connect only sdc to check whether the data is present.....

      This should never happen. You should not be doing this. RAID is a single subsystem and you should not be poking around in it. You are trying to do things that are not meant to be done. Don't attempt to look at individual disks. That is not meant to ever happen. Just because it can be done doesn't mean that it is a good idea.

      1 Reply Last reply Reply Quote 0
      • scottalanmillerS
        scottalanmiller
        last edited by

        If you want to find out if the data is all on the disk, use the MD stat file we looked at above, it tells you the status of the data on the disk.

        LakshmanaL 1 Reply Last reply Reply Quote 1
        • LakshmanaL
          Lakshmana @scottalanmiller
          last edited by

          @scottalanmiller Ok Sir.But my manager said that he needs to see the data to be present in the individual hard disk so only trying to see the data in individual disk.Why this cannot be done.Can you please say

          scottalanmillerS ? 3 Replies Last reply Reply Quote 0
          • scottalanmillerS
            scottalanmiller @Lakshmana
            last edited by

            @Lakshmana said:

            @scottalanmiller Ok Sir.But my manager said that he needs to see the data to be present in the individual hard disk so only trying to see the data in individual disk.Why this cannot be done.Can you please say

            Tell him "too bad." He doesn't understand what he is asking. What he wants will cause data loss. He needs to educate himself on RAID before he starts making demands. Just because a manager tells you to break things, doesn't mean that you should just break them. If he doesn't want the system to work, make sure everyone is aware that he is demanding that it be broken.

            1 Reply Last reply Reply Quote 0
            • ?
              A Former User @Lakshmana
              last edited by A Former User

              @Lakshmana said:

              @scottalanmiller Ok Sir.But my manager said that he needs to see the data to be present in the individual hard disk so only trying to see the data in individual disk.Why this cannot be done.Can you please say

              a RAID is not a backup. It's not meant to be used in this manner,

              LakshmanaL 1 Reply Last reply Reply Quote 1
              • scottalanmillerS
                scottalanmiller @Lakshmana
                last edited by

                @Lakshmana said:

                Why this cannot be done.

                Because you are breaking the RAID system. RAID is never meant to be torn apart and used in parts. The array is a singular storage system. When you break it apart not everything is there, and worse, the system now has failed components and needs to repair. Even if you found what you needed, now things are broken and files all have to be copied again.

                It's like Schrodinger's cat. If you open the box, you ruin everything.

                You need to use the RAID tools and let RAID do its job. If he doesn't trust the RAID, why are you using it?

                1 Reply Last reply Reply Quote 0
                • LakshmanaL
                  Lakshmana @A Former User
                  last edited by

                  @thecreativeone91 Whether that method is not possible with the one hard disk Sir.You said that the data loss may be occured but I tried the process by booting sda hard disk alone in rescue mode and seen the data with out any loss in the shell mode.

                  scottalanmillerS 1 Reply Last reply Reply Quote 0
                  • scottalanmillerS
                    scottalanmiller @Lakshmana
                    last edited by

                    @Lakshmana said:

                    @thecreativeone91 Whether that method is not possible with the one hard disk Sir.You said that the data loss may be occured but I tried the process by booting sda hard disk alone in rescue mode and seen the data with out any loss in the shell mode.

                    The data loss is not at this time, it is when you go to use the system again. What is the purpose of a storage system that you "break" to verify? That doesn't work. How will you use this once it is in production?

                    1 Reply Last reply Reply Quote 0
                    • ?
                      A Former User
                      last edited by

                      What was the point of this? if the raid failed you just put a new one in and rebuild it. The RAID Controller/Software will report when a raid is degraded, there is no need to "check it" manually.

                      scottalanmillerS 1 Reply Last reply Reply Quote 1
                      • scottalanmillerS
                        scottalanmiller @A Former User
                        last edited by

                        @thecreativeone91 said:

                        What was the point of this? if the raid failed you just put a new one in and rebuild it. The RAID Controller/Software will report when a raid is degraded, there is no need to "check it" manually.

                        "Checking it" is what will break things, too. It's just pointless, it is actually reckless and self defeating. If you want to ensure that the data is good, you can't do it this way.

                        LakshmanaL 2 Replies Last reply Reply Quote 0
                        • LakshmanaL
                          Lakshmana @scottalanmiller
                          last edited by

                          @scottalanmiller said:

                          you can't do it this way.

                          Ok Sir.I will explain this to my Manager and after that I acknowledge you sir

                          1 Reply Last reply Reply Quote 0
                          • LakshmanaL
                            Lakshmana @scottalanmiller
                            last edited by

                            @scottalanmiller Screenshot from 2015-03-02 19:04:32.png
                            Sir Please refer this image one person said me that RAID 1 member can be boooted by installing bootloader.Whether it is possible Sir.I don't know about that one small doubt came after this image seen

                            1 Reply Last reply Reply Quote 0
                            • scottalanmillerS
                              scottalanmiller
                              last edited by

                              Yes, in case of a broken RAID array you can install a bootloader, of course. But that doesn't change that what you are doing should not be done. This is for cases where the other drive is broken, not when a manager asks you to damage the system.

                              LakshmanaL 1 Reply Last reply Reply Quote 0
                              • LakshmanaL
                                Lakshmana @scottalanmiller
                                last edited by

                                @scottalanmiller Ok 😄 I understood.I went to Manager said that it cannot be done and the RAID configured device will lost the data and this is impossible.But he ask the explanation behind this and said to explain briefly

                                scottalanmillerS 1 Reply Last reply Reply Quote 0
                                • DashrenderD
                                  Dashrender
                                  last edited by

                                  I'm a bit lost - is @Lakshmana using hardware RAID or software RAID inside CentOS?

                                  If it's hardware RAID, and he pulls a drive, won't the system always work? because both drives are suppose to be identical?

                                  If it's software RAID, then I understand why he has failures.

                                  LakshmanaL scottalanmillerS 3 Replies Last reply Reply Quote 0
                                  • LakshmanaL
                                    Lakshmana @Dashrender
                                    last edited by

                                    @Dashrender Its Sofware RAID1

                                    1 Reply Last reply Reply Quote 0
                                    • scottalanmillerS
                                      scottalanmiller @Lakshmana
                                      last edited by

                                      @Lakshmana said:

                                      @scottalanmiller Ok 😄 I understood.I went to Manager said that it cannot be done and the RAID configured device will lost the data and this is impossible.But he ask the explanation behind this and said to explain briefly

                                      It's not that it is impossible, of course it can be done, the problem is is that you break the RAID device so the system is broken. So you are "checking" data that is no longer valid. You can verify that the RAID was working, but you've broken that RAID device and are starting over. So there was no value in checking it because now you have to rebuild it and.... check again? The act of checking it breaks the array.

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                                      • scottalanmillerS
                                        scottalanmiller @Dashrender
                                        last edited by

                                        @Dashrender said:

                                        I'm a bit lost - is @Lakshmana using hardware RAID or software RAID inside CentOS?

                                        Linux MD RAID.

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                                        • DashrenderD
                                          Dashrender
                                          last edited by

                                          No wonder pulling a drive causes this to fail.

                                          1 Reply Last reply Reply Quote 0
                                          • scottalanmillerS
                                            scottalanmiller @Dashrender
                                            last edited by

                                            @Dashrender said:

                                            If it's hardware RAID, and he pulls a drive, won't the system always work? because both drives are suppose to be identical?

                                            It's not hardware but hot swap that enables this. You can easily do this with MD RAID too, if done correctly. The problem is, the moment that you do this, the drive that you pull is out of date and no longer a valid member of the array. So anything that you "check" is now ruined AND you are running without RAID until you replace the drive and it rebuilds. So the thing that you check gets blown away the instant that you check it.

                                            DashrenderD 1 Reply Last reply Reply Quote 0
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