Geek Help - Linux RAID Questions

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  • crokett
    The Full Monte
    • Jan 2003
    • 10627
    • Mebane, NC, USA.
    • Ryobi BT3000
    #1

    Geek Help - Linux RAID Questions

    I got the machine I will use for the web/ssh/ftp/NAS and will put Linux on it. I will go with SATA HDDs but need a controller. The sales guy said for HW RAID get the 70.00 card but if I am not running RAID get the 15.00 one. It occurred to me that I could get 2 15.00 ones and 2 drives, run SW RAID and still come out ahead on the pricer adapter. I would run straight RAID-1 mirror, no parity checking so not that much additional load on the CPU.

    So my question - I know with Windows mirroring if the boot drive fails, all I have to do is tweak the boot.ini file and boot from the second drive. One shop I worked in booted Windows from floppy for this reason. If something was really hosed up, you could take the working drive, put it in another machine running Windows and still get the data. Does Linux do the same thing? Could I boot, say, off USB and if the primary drive takes a dive just load the install on the second one? Oh yeah, assuming I start with 1 HDD, can I add a 2nd and create the mirror without losing the data on the first one?
    Last edited by crokett; 02-18-2009, 08:00 PM.
    David

    The chief cause of failure in this life is giving up what you want most for what you want at the moment.
    Tags: None
    • gerti
      Veteran Member
      • Dec 2003
      • 2233
      • Minnetonka, MN, USA.
      • BT3100 "Frankensaw"
      #2
      No problem. This is one of the better articles I have found (and used):

      http://advosys.ca/viewpoints/2007/04...ubuntu-server/

      It is possible to set up a RAID1 with just one disk for starters, just add only 1 disk to the array.

        Comment

        • crokett
          The Full Monte
          • Jan 2003
          • 10627
          • Mebane, NC, USA.
          • Ryobi BT3000
          #3
          That is perfect, thanks for the link. I've decided what I actually will do is move the Windows install I have from the current machine to the new one. The new one has a slightly faster processor and more RAM. The current one maxes out at 1GB. After I get Windows stable on the new machine I will put Linux on the old one.
          David

          The chief cause of failure in this life is giving up what you want most for what you want at the moment.

            Comment

            • pierhogunn
              Veteran Member
              • Sep 2003
              • 1567
              • Harrisburg, NC, USA.
              #4
              after working with both SW raid and HW raid, I would go with HW raid any day of the week. if HW raid breaks you replace the card, and away you go, if sw raid breaks... well lets just say the therapy is helping with the PTSD from rebuilding mission critical drives and sw raid sets

              **EDIT**

              On second thought, I would like to amend my previous statement and add that:

              I would rather be savagely, and repeatedly raped by a pack of rabid wild mountain gorillas than spend time rebuilding a software raid, especially one that contains the root directories of the system in question, while I am quite adept at it, i never, ever want to do it again. and since when did it ever, EVER, become a good idea to put your boot drive into a raid 0 or raid 5 set?

              Hardware raid1 on a set of boot drives is a great idea!
              Last edited by pierhogunn; 02-19-2009, 11:35 AM. Reason: rethought my post
              It's Like I've always said, it's amazing what an agnostic can't do if he dosent know whether he believes in anything or not

              Monty Python's Flying Circus

              Dan in Harrisburg, NC

                Comment

                • LinuxRandal
                  Veteran Member
                  • Feb 2005
                  • 4890
                  • Independence, MO, USA.
                  • bt3100
                  #5
                  What about buying two identical drives, placing your OS, on one, and ghosting to the other. Then you raid your home directory (as long as it isn't encrypted, you should be able to mount and read it on another machine), and back up your preferences/settings/bookmarks to the home directory?

                  Your OS drive dies, you swap and import your preferences.
                  She couldn't tell the difference between the escape pod, and the bathroom. We had to go back for her.........................Twice.

                    Comment

                    • rjwaldren
                      Established Member
                      • Nov 2007
                      • 368
                      • Fresno, CA
                      #6
                      Remember that a hardware RAID will be transparent under linux whereas software will require additional set up and I would recommend having at least your boot directory on a solo drive or partition not in the array. (with a good backup).

                      Personally I'd go with the hardware version. What HW raid card are you looking at for $70.

                        Comment

                        • crokett
                          The Full Monte
                          • Jan 2003
                          • 10627
                          • Mebane, NC, USA.
                          • Ryobi BT3000
                          #7
                          I've had extensive experience with SW and HW RAID and I am aware of the challenges. Believe you me, I've seen many a HW RAID Array go south. The most experience I've had with SW RAID is Windows NT/2000. It might have changed since then but back in those days, Windows would mirror a drive. If the primary broke, you could either tweak the boot.ini and boot from floppy to the secondary or put the seccondary in another PC with a running Windows install, tweak the boot.ini and then boot from the secondary back in the original machine. I actually used this more than once to move data from one HDD to another when moving/upgrading PCs. I even moved an install from straight SCSI to HW RAID by configuring the array, loading the controller driver in Windows and mirroring to the RAID Array. Then broke the mirror, shut down the PC and removed the SCSI drive, reooted and Windows was happy on the RAID Array.

                          I wanted to know if Linux will allow me to do the same thing with a simple mirror. Either boot to the surviving drive or be able to read the data under a new install. I guess I have some testing to do.

                          The RAID adapter I was looking at is a Promise FastTrak and I wasn't really looking as much as I saw it in the store.
                          David

                          The chief cause of failure in this life is giving up what you want most for what you want at the moment.

                            Comment

                            • pierhogunn
                              Veteran Member
                              • Sep 2003
                              • 1567
                              • Harrisburg, NC, USA.
                              #8
                              my experience is with solaris 2.5, 6, 7 , 8 and 9... still feel a little dirty, veritas, ODS, and ODS+
                              It's Like I've always said, it's amazing what an agnostic can't do if he dosent know whether he believes in anything or not

                              Monty Python's Flying Circus

                              Dan in Harrisburg, NC

                                Comment

                                • rjwaldren
                                  Established Member
                                  • Nov 2007
                                  • 368
                                  • Fresno, CA
                                  #9
                                  Okay, it looks like the link above covers it pretty well and a few experiments is all it should take. Honestly I've never lost a Linux RAID1, just experimented like you, too long ago to trust that I could do it from memory. I've lost a few under Windows and LVM's under Linux.

                                  SW takes a bit more fiddling but it's getting better as more "fake RAID" products now have in-kernel support.

                                    Comment

                                    • gerti
                                      Veteran Member
                                      • Dec 2003
                                      • 2233
                                      • Minnetonka, MN, USA.
                                      • BT3100 "Frankensaw"
                                      #10
                                      For smaller setups I much prefer SW raids, especially when I need to remote monitor them. Back then when I last tried them most hardware raids had to be booted into their BIOS or some such to do anything.

                                      The trick with any raid (but particularly software RAID) is early on in the install, when you don't have spent much time in installing software or mission critical data, work out your failure scenarios, and write detailed instructions for your specific setup. That way you can experiment without fear, and work it all out so you have it handy should a drive break. I have used SW raid since 15 years, on about 100 linux servers, and it has served me very well.

                                      Edit: we are talking RAID 1 here. Other then for some very specific cases, RAID 0 is a very bad idea, they basically double chances of failure and provide 0 backup. And these days there are very few cases where RAID 5 even makes sense.
                                      Last edited by gerti; 02-19-2009, 11:11 PM.

                                        Comment

                                        • crokett
                                          The Full Monte
                                          • Jan 2003
                                          • 10627
                                          • Mebane, NC, USA.
                                          • Ryobi BT3000
                                          #11
                                          Originally posted by gerti

                                          Edit: we are talking RAID 1 here. Other then for some very specific cases, RAID 0 is a very bad idea, they basically double chances of failure and provide 0 backup. And these days there are very few cases where RAID 5 even makes sense.
                                          Most of my customers who measure disk space in terabytes either use RAID 10 or RAID 50. A very few will still use RAID 5.

                                          I found this link which shows exactly what I want to do:

                                          http://www.howtoforge.com/how-to-ins...software-raid1
                                          David

                                          The chief cause of failure in this life is giving up what you want most for what you want at the moment.

                                            Comment

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