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Use Of Shared Storage In High Availability Arrays?

Posted by Cliff on from the figuring-things-out dept.

urbanjunkie asks: "I want to ensure my web site/database farm/whatever is as available as possible, so I checked out many HA (High Availability) packages for Linux. It seems that they -all- seem to want me to use shared storage. I don't want to use shared storage since it moves the point of failure to the disk array. I know that the disk array can be RAIDed etc, but what about a fire, power loss and any of the other things that can go wrong? I'd prefer to have something that replicated changes made to one disk to another disk located in a separate PC that may well be in a location 100 metres away. Is there anything open sourced that can do this?"

8 of 18 comments (clear)

  1. Try OpenAFS by Raleel · · Score: 2

    I know that afs has disreplication abilities. I'm by no means an expert on it, however

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    -- Who is the bigger fool? The fool or the fool who follows him? --
    1. Re:Try OpenAFS by Raleel · · Score: 2

      I should be smacked..that's disk replication..good lord, save me

      --
      -- Who is the bigger fool? The fool or the fool who follows him? --
  2. Stick with shared storage... by autocracy · · Score: 2
    If you're worried about any single point of failure, run a Sun T3 storage array. The only single point of failure there is the drive controller, which hardly fails. And since we're into eliminating ALL failure points, buy two. You can link them together so that even if one controller fails, the controller on the other machine kicks in. Zero points of failure!

    For the sake of specs, the thing takes 9 SCSI disks, using FC/AL for linkup, and works with Linux and Solaris (among other systems I believe). Placing 2 together DOES NOT make a RAID5+1 array, the whole thing is straigh RAID5. The systems also have 256 MB of RAM to remove the RAID5 write penalty. Should a catastrophic failure occcur (all power to the box kicks), internal UPSes will dump the info in the RAM to the disks and power down correctly.

    The investment is definitely worth it, and makes things easier than other systems. As for fire damage, get a Halon system and BACKUP YOUR DATA!

    If you're really paranoid, you can seperate the boxes a little...

    My karma's bigger than yours!

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    SIG: HUP
    1. Re:Stick with shared storage... by Jason+Pollock · · Score: 2

      I don't think that you really get it. It _still_ has a _single_ point of failure, and it's a pretty large point, the whole box. Urbanjunkie is asking for a solution that will allow service to continue even if a whole box (any box) is destroyed.

      Think earthquake. Then design a network layout and set of systems that would withstand the total destruction of any system in the network. That's what urbanjunkie is asking for.

      Database replication can be nasty business. It all comes down to the failure modes. Things like distributed transactions can have some pretty nasty ones. No, I don't have a solution. :) If your period between updates is high, you can try having one authoritative system. You perform all your updates to it, and then periodically shut it down and copy the files to the remote servers.

      Jason Pollock
    2. Re:Stick with shared storage... by weave · · Score: 3
      EMC has storage that can be mirrored over a fiber or even copper at speeds as low as 100 Mbps allowing a mirrored HA array to be stashed off-site. It tracks disk writes and duplicates them at the other site. It can even batch up the sync writes to occur in off-peak hours if desired.

      I guess it's how much availability you want. That last 0.001% drives costs through the roof. Many modern disk arrays have everything redundant and hot swappable, including not just disk modules, but power supplies, fans, and controllers.

      Set up a nice HA disk array and cluster the servers and you too can run all of your critical services on one subnet!

  3. Yes, there is. by pete-classic · · Score: 2

    I'd prefer to have something that replicated changes made to one disk to another disk located in a separate PC that may well be in a location 100 metres away. Is there anything open sourced that can do this?

    Yes, rsync. http://rsync.samba.org

    -Peter


    "There is no number '1.'"

  4. EMC by crow · · Score: 2

    If you want the ultimate in high-availability storage, go with EMC. You get the highest possible level of reliability within one box, and you can get remote mirroring to another machine room in another building if need be.

    Disclaimer: I work for EMC.

  5. Solaris HA solution by schnurble · · Score: 2

    I know he asked for a Linux solution, but the truth is that sometimes Linux just isn't the best tool for the job.

    Currently, we're running a pair of Sun E4500's (4 CPU 6 gig 2 disk boards 2 IO boards) connected to a pair of Sun StorEDGE A5200 disk arrays by FCAL. Each box has 2 fiber connections to each array, for a max throughput to the box of 2gbit. The 4500's are running Solaris 7 for OS, Veritas Volume Manager for managing disk storage, and Veritas Cluster Server for HA management of Oracle 8.

    Veritas won't let both machines mount the disks at the same time (which would be bad anyway), and it does a rather good job of managing things. Recently when we had a cpu die in the primary machine, the cluster failed over and had Oracle up (and running recovery) in 1 minute 3 seconds. Not bad, considering the other box rebooted itself and didn't shut Oracle down cleanly.

    -j

    --
    "To err is human, to forgive is simply not my policy." --root