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    LVM Question

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    linux lvm
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    • stacksofplates
      stacksofplates last edited by

      Ok this might be a dumb question. What's a scenario where you would span a volume group over multiple disks? The only thing I could think of was needing extra space, but why not just increase the size of your disk?

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

        I just thought of this. Possibly MBR disk size lmitations?

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

          @johnhooks said:

          The only thing I could think of was needing extra space, but why not just increase the size of your disk?

          There are a great many cases when you cannot just increase the size of your disks. It is actually extremely common in the enterprise space that many small LUNs be handed to the system and LVM be expected to bind them into a single storage unit.

          stacksofplates 2 Replies Last reply Reply Quote 2
          • stacksofplates
            stacksofplates @scottalanmiller last edited by

            @scottalanmiller said:

            @johnhooks said:

            The only thing I could think of was needing extra space, but why not just increase the size of your disk?

            There are a great many cases when you cannot just increase the size of your disks. It is actually extremely common in the enterprise space that many small LUNs be handed to the system and LVM be expected to bind them into a single storage unit.

            What's the advantage to doing that over RAID 0 and then making one PV?

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

              @johnhooks said:

              What's the advantage to doing that over RAID 0 and then making one PV?

              Reliability. If one slice fails, RAID 0 would hose the full filesystem. With a span there is a lot less "one blip spells total disaster."

              stacksofplates 1 Reply Last reply Reply Quote 1
              • stacksofplates
                stacksofplates @scottalanmiller last edited by

                @scottalanmiller said:

                @johnhooks said:

                What's the advantage to doing that over RAID 0 and then making one PV?

                Reliability. If one slice fails, RAID 0 would hose the full filesystem. With a span there is a lot less "one blip spells total disaster."

                I didn't realize it was more reliable than RAID 0. Thanks!

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

                  @scottalanmiller said:

                  @johnhooks said:

                  The only thing I could think of was needing extra space, but why not just increase the size of your disk?

                  There are a great many cases when you cannot just increase the size of your disks. It is actually extremely common in the enterprise space that many small LUNs be handed to the system and LVM be expected to bind them into a single storage unit.

                  @scottalanmiller said:

                  @johnhooks said:

                  The only thing I could think of was needing extra space, but why not just increase the size of your disk?

                  There are a great many cases when you cannot just increase the size of your disks. It is actually extremely common in the enterprise space that many small LUNs be handed to the system and LVM be expected to bind them into a single storage unit.

                  Plus I guess if you're not in control of the Hypervisor then you'd have to make due with what you're given.

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

                    @johnhooks said:

                    @scottalanmiller said:

                    @johnhooks said:

                    What's the advantage to doing that over RAID 0 and then making one PV?

                    Reliability. If one slice fails, RAID 0 would hose the full filesystem. With a span there is a lot less "one blip spells total disaster."

                    I didn't realize it was more reliable than RAID 0. Thanks!

                    It's not great, the filesystem tends to be unhappy when parts disappear. But if you have 100 slices and one vanishes, likely only a few files will be impacted rather than everything. Not always, but safer at least.

                    stacksofplates 1 Reply Last reply Reply Quote 1
                    • stacksofplates
                      stacksofplates @scottalanmiller last edited by

                      @scottalanmiller said:

                      @johnhooks said:

                      @scottalanmiller said:

                      @johnhooks said:

                      What's the advantage to doing that over RAID 0 and then making one PV?

                      Reliability. If one slice fails, RAID 0 would hose the full filesystem. With a span there is a lot less "one blip spells total disaster."

                      I didn't realize it was more reliable than RAID 0. Thanks!

                      It's not great, the filesystem tends to be unhappy when parts disappear. But if you have 100 slices and one vanishes, likely only a few files will be impacted rather than everything. Not always, but safer at least.

                      That's kind of awesome. I didn't realize it was that much more reliable.

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

                        Also if one slice is slow and the others are fast, you don't have to wait on the one to put blocks together. So temperamental delays are less impactful.

                        1 Reply Last reply Reply Quote 1
                        • stacksofplates
                          stacksofplates last edited by

                          And if you have mismatched sizes you would lose space with RAID 0. And can't grow RAID 0 either.

                          Ha I knew it was a dumb question.

                          scottalanmiller 1 Reply Last reply Reply Quote 1
                          • scottalanmiller
                            scottalanmiller @stacksofplates last edited by

                            @johnhooks said:

                            And if you have mismatched sizes you would lose space with RAID 0. And can't grow RAID 0 either.

                            Ha I knew it was a dumb question.

                            Very true as well.

                            1 Reply Last reply Reply Quote 0
                            • travisdh1
                              travisdh1 last edited by

                              I :heart: LVM

                              1 Reply Last reply Reply Quote 2
                              • StrongBad
                                StrongBad last edited by

                                LVM is awesome, it is a great tool.

                                stacksofplates 1 Reply Last reply Reply Quote 2
                                • stacksofplates
                                  stacksofplates @StrongBad last edited by

                                  @StrongBad said:

                                  LVM is awesome, it is a great tool.

                                  I use it all the time. Snapshots are awesome. I've just never needed to use multiple disks and didn't think of the above scenarios when you would have multiple PVs.

                                  1 Reply Last reply Reply Quote 1
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