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    Power Loss Followthrough

    IT Discussion
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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.

      1 Reply Last reply Reply Quote 0
      • 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.

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

            that's what I figured.

            Thanks

            1 Reply Last reply Reply Quote 0
            • StrongBadS
              StrongBad
              last edited by

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

              1 Reply Last reply Reply Quote 0
              • 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
                        • StrongBadS
                          StrongBad @BRRABill
                          last edited by

                          @BRRABill said:

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

                          That would depend on the same factors as if you didn't have a RAID controller. Enterprise class drives are about support and write lifespans. That you have RAID or do not have RAID does not affect that in a significant way.

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

                            @StrongBad said:

                            That would depend on the same factors as if you didn't have a RAID controller. Enterprise class drives are about support and write lifespans. That you have RAID or do not have RAID does not affect that in a significant way.

                            The manufacturers always seem to harp on the power circuitry.

                            Perhaps for desktops?

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                            • scottalanmillerS
                              scottalanmiller
                              last edited by

                              Lots of people get them and don't have RAID cards in front of them. And you do want the drive to get stuff to disk before reporting to the RAID card. But pretty much, it's all in the controller

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                              • BRRABillB
                                BRRABill
                                last edited by

                                Still would always recommend enterprise level SSDs for servers though, right?

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

                                  @BRRABill said:

                                  Still would always recommend enterprise level SSDs for servers though, right?

                                  No, they are rarely recommended except for getting integrated support. In almost any situation where you would be in a position to choose, you'd choose consumer.

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

                                    @scottalanmiller said:

                                    No, they are rarely recommended except for getting integrated support. In almost any situation where you would be in a position to choose, you'd choose consumer.

                                    But only if behind a RAID controller with cache though, right?

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

                                      @BRRABill said:

                                      @scottalanmiller said:

                                      No, they are rarely recommended except for getting integrated support. In almost any situation where you would be in a position to choose, you'd choose consumer.

                                      But only if behind a RAID controller with cache though, right?

                                      Why would RAID matter?

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                                      • scottalanmillerS
                                        scottalanmiller
                                        last edited by

                                        A RAID cache is always recommended .... for SSD because it reduces write wear, for Winchesters because it adds so much performance.

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                                        • BRRABillB
                                          BRRABill
                                          last edited by

                                          My line of though was

                                          consumer SSD theoreticallly has less writes
                                          the RAID controller saves, as you said, a ton of writes

                                          hence if you get a consumer drive, you;d want to pair it with the RAID controller with cache to save the writes. we had a whole thread on that.

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

                                            @BRRABill said:

                                            hence if you get a consumer drive, you;d want to pair it with the RAID controller with cache to save the writes. we had a whole thread on that.

                                            But having a RAID card is the starting assumption for any important workload. The choice of consumer versus enterprise is not driven by it because it is an assumed starting point.

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