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    Power Loss Followthrough

    Scheduled Pinned Locked Moved IT Discussion
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    • scottalanmillerS
      scottalanmiller
      last edited by

      The issue is components that do caching. It's all about either not having storage do anything or getting confirmation that writes have completed and will persist.

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      • J
        Jason Banned @BRRABill
        last edited by

        @BRRABill said:

        I mean, if the power supply goes, doesn't the motherboard, etc., also go?

        At what point does this all become moot as components that aren't protected by power loss circuitry get involved and fail?

        This isn't about continuing to process data. This is about writing data to the physical disks that have already been sent to the raid controller and is currently in volatile memory, if this is not copied to a disk before it looses power all of this data will be lost.

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        • scottalanmillerS
          scottalanmiller
          last edited by

          Data that systems believe has been recorded. Transactions that something thinks has been processed but hasn't finished, in actuality.

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          • BRRABillB
            BRRABill
            last edited by

            But if the power goes off (via power supply loss or whatever) wouldn't data being sent TO the controler/cache already be interrupted in mid stream?

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

              @BRRABill said:

              But if the power goes off (via power supply loss or whatever) wouldn't data being sent TO the controler/cache already be interrupted in mid stream?

              Data sent but not received isn't an issue as nothing believes that it has arrived yet. It is the data that has arrived at the controlled but has not gone to disk yet that is the issue.

              dafyreD 1 Reply Last reply Reply Quote 1
              • dafyreD
                dafyre @scottalanmiller
                last edited by

                @scottalanmiller said:

                @BRRABill said:

                But if the power goes off (via power supply loss or whatever) wouldn't data being sent TO the controler/cache already be interrupted in mid stream?

                Data sent but not received isn't an issue as nothing believes that it has arrived yet. It is the data that has arrived at the controlled but has not gone to disk yet that is the issue.

                I thought this was why some raid cards have their own batteries?

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

                  @dafyre said:

                  I thought this was why some raid cards have their own batteries?

                  Exactly. That what we are explaining the need for 🙂

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                  • BRRABillB
                    BRRABill
                    last edited by

                    So once the system (aka the motherboard) sends it to the controller, it assumes it has been written.

                    So if it never hits the controller, it's like it never happened?

                    scottalanmillerS 1 Reply Last reply Reply Quote 0
                    • BRRABillB
                      BRRABill
                      last edited by

                      P.S. I am assuming the H710 (512MB) has a battery?

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                      • scottalanmillerS
                        scottalanmiller
                        last edited by

                        Should be flash backed and not volatile.

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                        • scottalanmillerS
                          scottalanmiller @BRRABill
                          last edited by

                          @BRRABill said:

                          So if it never hits the controller, it's like it never happened?

                          Right, the controller is the first component that reports back up the stack that the "data has been written to disk." Things up the stack need to be able to trust that report.

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                          • DashrenderD
                            Dashrender
                            last edited by

                            I want to add something to this,

                            I'm assuming that the battery backup or non volatile Flash don't write anything while the power is out. because, the RAID controller battery doesn't have enough power to keep the drives spinning, and obviously the non volatile Flash has no power at all.
                            Instead, these backups keep the RAID data alive until the system comes back online and then finishes writing the data to disk.

                            Right?

                            brianlittlejohnB 1 Reply Last reply Reply Quote 2
                            • brianlittlejohnB
                              brianlittlejohn @Dashrender
                              last edited by

                              @Dashrender Correct.

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                              • DashrenderD
                                Dashrender
                                last edited by

                                that's what I figured.

                                Thanks

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                                • StrongBadS
                                  StrongBad
                                  last edited by

                                  Yes, they just maintain "stasis" until the power comes back on.

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                                  • BRRABillB
                                    BRRABill
                                    last edited by

                                    Where does the "power loss circuitry" in an enterpise class SSD fall into this?

                                    DashrenderD scottalanmillerS 2 Replies Last reply Reply Quote 0
                                    • DashrenderD
                                      Dashrender @BRRABill
                                      last edited by

                                      @BRRABill said:

                                      Where does the "power loss circuitry" in an enterpise class SSD fall into this?

                                      If I were to guess, I'd say the same as the RAID controllers. The data comes in and is written to some non volatile place, but not reported as finished being written to the RAID controller until it's done writing to the final destination on the SSD.

                                      MattSpellerM 1 Reply Last reply Reply Quote 1
                                      • MattSpellerM
                                        MattSpeller @Dashrender
                                        last edited by

                                        @Dashrender said:

                                        @BRRABill said:

                                        Where does the "power loss circuitry" in an enterpise class SSD fall into this?

                                        If I were to guess, I'd say the same as the RAID controllers. The data comes in and is written to some non volatile place, but not reported as finished being written to the RAID controller until it's done writing to the final destination on the SSD.

                                        They have capacitors (super caps?) in them. These act like a battery.

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                                        • scottalanmillerS
                                          scottalanmiller @BRRABill
                                          last edited by

                                          @BRRABill said:

                                          Where does the "power loss circuitry" in an enterpise class SSD fall into this?

                                          It's redundant. Normally RAID controllers disable drive caches.

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                                          • BRRABillB
                                            BRRABill
                                            last edited by

                                            If you have an SSD behind a RAID controller, do you need Enterprise class then?

                                            StrongBadS 1 Reply Last reply Reply Quote 0
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