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    Large or small Raid 5 with SSD

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    • ObsolesceO
      Obsolesce @Donahue
      last edited by Obsolesce

      @Donahue said in Large or small Raid 5 with SSD:

      Live optics says I've got ~3k IOPS peak between all my existing hosts, and ~800 at 95%.

      @Donahue said in Large or small Raid 5 with SSD:

      A simple raid 5 with like 4x3.84TB SSD's is appealing

      That'll be just dandy. Depends on the SSDs, but that's at least 11k IOPS (edit: at 90% write). Still a 16TB RAID5 though, and rebuild performance is 30% by default.

      1 Reply Last reply Reply Quote 0
      • DonahueD
        Donahue
        last edited by

        @Obsolesce said in Large or small Raid 5 with SSD:

        @Donahue said in Large or small Raid 5 with SSD:

        Live optics says I've got ~3k IOPS peak between all my existing hosts, and ~800 at 95%.

        @Donahue said in Large or small Raid 5 with SSD:

        A simple raid 5 with like 4x3.84TB SSD's is appealing

        That'll be just dandy. Depends on the SSDs, but that's at least 11k IOPS. Still a 16TB RAID5 though, and rebuild performance is 30% by default.

        what do you mean by ... and rebuild performance is 30% by default...?

        ObsolesceO 1 Reply Last reply Reply Quote 0
        • ObsolesceO
          Obsolesce @Donahue
          last edited by

          @Donahue said in Large or small Raid 5 with SSD:

          @Obsolesce said in Large or small Raid 5 with SSD:

          @Donahue said in Large or small Raid 5 with SSD:

          Live optics says I've got ~3k IOPS peak between all my existing hosts, and ~800 at 95%.

          @Donahue said in Large or small Raid 5 with SSD:

          A simple raid 5 with like 4x3.84TB SSD's is appealing

          That'll be just dandy. Depends on the SSDs, but that's at least 11k IOPS. Still a 16TB RAID5 though, and rebuild performance is 30% by default.

          what do you mean by ... and rebuild performance is 30% by default...?

          On Dells, when a drive rebuilds, it does it at 30% capabilities by default. I assume to prevent production services coming to a crawl. You can change it though.

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

            @Obsolesce said in Large or small Raid 5 with SSD:

            @Donahue said in Large or small Raid 5 with SSD:

            @Obsolesce said in Large or small Raid 5 with SSD:

            @Donahue said in Large or small Raid 5 with SSD:

            Live optics says I've got ~3k IOPS peak between all my existing hosts, and ~800 at 95%.

            @Donahue said in Large or small Raid 5 with SSD:

            A simple raid 5 with like 4x3.84TB SSD's is appealing

            That'll be just dandy. Depends on the SSDs, but that's at least 11k IOPS. Still a 16TB RAID5 though, and rebuild performance is 30% by default.

            what do you mean by ... and rebuild performance is 30% by default...?

            On Dells, when a drive rebuilds, it does it at 30% capabilities by default. I assume to prevent production services coming to a crawl. You can change it though.

            30% of capabilities, not 30% speed, though. So it is difficult to calculate.

            1 Reply Last reply Reply Quote 0
            • DonahueD
              Donahue
              last edited by

              Ok, lets add a layer to this. Lets assume the raid 5 will lose a disk. Do I run with no spare of any kind, and when it fails, then buy a replacement and switch it out? Is the URE risk primarily during rebuild, or anytime it is in a degraded state? I know that SSD's are generally an order of magnitude (or two) safer in this regard, but I want to have this planned out ahead of time.

              scottalanmillerS 2 Replies Last reply Reply Quote 0
              • DonahueD
                Donahue
                last edited by

                also, am I right to assume that network contention can influence IOPS?

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

                  @Donahue said in Large or small Raid 5 with SSD:

                  Is the URE risk primarily during rebuild, or anytime it is in a degraded state?

                  URE is quite nominal on SSDs typically. Not zero, but not like you are used to, either.

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

                    @Donahue said in Large or small Raid 5 with SSD:

                    also, am I right to assume that network contention can influence IOPS?

                    Resulting IOPS to a third party service, but not IOPS themselves.

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

                      But I know that you don't have a SAN, so in your case the answer is no.

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

                        @Donahue said in Large or small Raid 5 with SSD:

                        Ok, lets add a layer to this. Lets assume the raid 5 will lose a disk. Do I run with no spare of any kind, and when it fails, then buy a replacement and switch it out?

                        You can, lots of places with four hour SLA hardware replacement plans do that. I wouldn't do that without a warranty to cover the replacements, though.

                        1 Reply Last reply Reply Quote 0
                        • DonahueD
                          Donahue @scottalanmiller
                          last edited by

                          @scottalanmiller said in Large or small Raid 5 with SSD:

                          @Donahue said in Large or small Raid 5 with SSD:

                          Is the URE risk primarily during rebuild, or anytime it is in a degraded state?

                          URE is quite nominal on SSDs typically. Not zero, but not like you are used to, either.

                          but is the risk only present one I initiate a rebuild? As in, if a primary failure occurs, do I have time to assess my options before starting? I am basically trying to figure out if I should buy 4 or 5 drives. I know you said earlier that with raid 5, you may as well add that 5th drive to the array and make it a raid 6 as opposed to sitting on the shelf.

                          scottalanmillerS JaredBuschJ 3 Replies Last reply Reply Quote 0
                          • DonahueD
                            Donahue
                            last edited by

                            I am probably looking at more like next day replacement

                            1 Reply Last reply Reply Quote 1
                            • DonahueD
                              Donahue @scottalanmiller
                              last edited by

                              @scottalanmiller said in Large or small Raid 5 with SSD:

                              @Donahue said in Large or small Raid 5 with SSD:

                              also, am I right to assume that network contention can influence IOPS?

                              Resulting IOPS to a third party service, but not IOPS themselves.

                              It will certainly improve latency. That synology is averaging 14.6ms reads, with spikes over 280. writes are averaging 4.5ms with spikes over 200.

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

                                @Donahue said in Large or small Raid 5 with SSD:

                                @scottalanmiller said in Large or small Raid 5 with SSD:

                                @Donahue said in Large or small Raid 5 with SSD:

                                Is the URE risk primarily during rebuild, or anytime it is in a degraded state?

                                URE is quite nominal on SSDs typically. Not zero, but not like you are used to, either.

                                but is the risk only present one I initiate a rebuild? As in, if a primary failure occurs, do I have time to assess my options before starting? I am basically trying to figure out if I should buy 4 or 5 drives. I know you said earlier that with raid 5, you may as well add that 5th drive to the array and make it a raid 6 as opposed to sitting on the shelf.

                                Yes, but if you are waiting, that's when you create the risk of a second drive failing. Because your time exposure goes from a few hours to potentially days. That's a lot of expansion.

                                1 Reply Last reply Reply Quote 0
                                • DonahueD
                                  Donahue
                                  last edited by

                                  just to clarify, we are talking about two different risks, with two different triggers, correct? The risk of a second disk failure while degraded, which is triggered the moment the first disk dies. The second risk (and less so for SSD) is URE, but my question is does this risk only trigger once you initiate a rebuild? Because it is the rebuild itself that is trying to read the unreadable block during its parity calculation?

                                  scottalanmillerS 1 Reply Last reply Reply Quote 0
                                  • JaredBuschJ
                                    JaredBusch @Donahue
                                    last edited by

                                    @Donahue said in Large or small Raid 5 with SSD:

                                    @scottalanmiller said in Large or small Raid 5 with SSD:

                                    @Donahue said in Large or small Raid 5 with SSD:

                                    Is the URE risk primarily during rebuild, or anytime it is in a degraded state?

                                    URE is quite nominal on SSDs typically. Not zero, but not like you are used to, either.

                                    but is the risk only present one I initiate a rebuild? As in, if a primary failure occurs, do I have time to assess my options before starting? I am basically trying to figure out if I should buy 4 or 5 drives. I know you said earlier that with raid 5, you may as well add that 5th drive to the array and make it a raid 6 as opposed to sitting on the shelf.

                                    I never do hot spare. If you are going to have it plugged in, use it. Make it a RAID 6.

                                    1 Reply Last reply Reply Quote 2
                                    • scottalanmillerS
                                      scottalanmiller @Donahue
                                      last edited by

                                      @Donahue said in Large or small Raid 5 with SSD:

                                      just to clarify, we are talking about two different risks, with two different triggers, correct? The risk of a second disk failure while degraded, which is triggered the moment the first disk dies. The second risk (and less so for SSD) is URE, but my question is does this risk only trigger once you initiate a rebuild? Because it is the rebuild itself that is trying to read the unreadable block during its parity calculation?

                                      The URE risk only triggers once you trigger a rebuild, but the shift risk happens the moment you delay replacing the disk. You can't win through that thought process.

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

                                        @Donahue said in Large or small Raid 5 with SSD:

                                        I know you said earlier that with raid 5, you may as well add that 5th drive to the array and make it a raid 6 as opposed to sitting on the shelf.

                                        Not "might as well", but "had better make sure you do." Difference in risk is astronomic. If you are even thinking hot spare is an option, we've not explain adequately how it works.

                                        DashrenderD DonahueD 2 Replies Last reply Reply Quote 1
                                        • DashrenderD
                                          Dashrender @scottalanmiller
                                          last edited by

                                          @scottalanmiller said in Large or small Raid 5 with SSD:

                                          @Donahue said in Large or small Raid 5 with SSD:

                                          just to clarify, we are talking about two different risks, with two different triggers, correct? The risk of a second disk failure while degraded, which is triggered the moment the first disk dies. The second risk (and less so for SSD) is URE, but my question is does this risk only trigger once you initiate a rebuild? Because it is the rebuild itself that is trying to read the unreadable block during its parity calculation?

                                          The URE risk only triggers once you trigger a rebuild, but the shift risk happens the moment you delay replacing the disk. You can't win through that thought process.

                                          How is the URE not a risk the instant the first drive fails. Can't a URE happen during normal disk operation? i.e. you're in degraded status - and while reading before starting the rebuild, hit an URE?

                                          travisdh1T scottalanmillerS 2 Replies Last reply Reply Quote 0
                                          • DashrenderD
                                            Dashrender @scottalanmiller
                                            last edited by

                                            @scottalanmiller said in Large or small Raid 5 with SSD:

                                            @Donahue said in Large or small Raid 5 with SSD:

                                            I know you said earlier that with raid 5, you may as well add that 5th drive to the array and make it a raid 6 as opposed to sitting on the shelf.

                                            Not "might as well", but "had better make sure you do." Difference in risk is astronomic. If you are even thinking hot spare is an option, we've not explain adequately how it works.

                                            Assuming the performance hit is as low as Scott claims (and I'm sure he's right) then there would be no reason to not put the protection in place now - you have the drive, just use it. Sitting it on the shelf introduces risk you don't need to take - the amount of time for you to be notified, and then act upon that notification before a second drive fails. Why expose that risk when you don't have to.

                                            1 Reply Last reply Reply Quote 1
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