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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
      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.

                                    1 Reply Last reply Reply Quote 0
                                    • 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.

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

                                            @scottalanmiller said:

                                            @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.

                                            I completely understand that - and maybe @Lakshmana does as well. So the act of testing this only proves the system will continue to function while the system is running, but probably won't survive if you reboot the system or power it down and back up. And once you put reattach a drive, even if it's the original one you pulled for the test, it has to be completely rebuilt. But pulling the drive does prove if the system is working or not.

                                            scottalanmillerS LakshmanaL 2 Replies Last reply Reply Quote 0
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