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Exchange Transaction Logs on RAID 5

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  • Exchange Transaction Logs on RAID 5

    We have a client who wants to have Exchange 2003 Standard installed on new server they bought. The server has plenty of memory and disk space, however it is a RAID 5 configured as 1 physical disk. The total amout of users is probally going to peak at 35, most of which are light users.

    Considering that the array has fault tolerance, will it matter if the transaction log files are on the same disk? (They also have backup software that will clear the files after a full backup.)

    Is performance an issue with so few users?

    Many thanks in advance.

  • #2
    Re: Exchange Transaction Logs on RAID 5

    With a single array you are going to gain nothing.
    There are two main reasons for putting the transaction logs on to a different array/drive:

    1. Performance.
    This the major reason as even on a small number of users, when Exchange does anything it will be writing to both the transaction logs and the database at the same time.

    2. Disaster Recovery.
    By having the logs separate from the database, you can theoretically lose the database, restore from backup then replay the transaction logs.

    You haven't said how many disks were installed, but if possible I would suggest that they are split differently to try and maximise the performance. Having everything on a single RAID 5 array could actually cause a performance hit.

    Simon.
    --
    Simon Butler
    Exchange MVP

    Blog: http://blog.sembee.co.uk/
    More Exchange Content: http://exchange.sembee.info/
    Exchange Resources List: http://exbpa.com/
    In the UK? Hire me: http://www.sembee.co.uk/

    Sembee is a registered trademark, used here with permission.

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    • #3
      Re: Exchange Transaction Logs on RAID 5

      Thanks for the response. There are 3 disks in the array, which are hot-pluggable.

      Does that matter?

      Comment


      • #4
        Re: Exchange Transaction Logs on RAID 5

        You aren't going to gain anything from that.

        Ideally you need a minimum of five disks, so that you can mirror one array (partitioned twice) and have a single RAID 5 array.

        The only thing you have from that configuration is fault tolerance. The servers performance will be dire because everything is on the same hard disk.
        Even at home I have my transaction logs and database on separate disks.

        Simon.
        --
        Simon Butler
        Exchange MVP

        Blog: http://blog.sembee.co.uk/
        More Exchange Content: http://exchange.sembee.info/
        Exchange Resources List: http://exbpa.com/
        In the UK? Hire me: http://www.sembee.co.uk/

        Sembee is a registered trademark, used here with permission.

        Comment


        • #5
          Re: Exchange Transaction Logs on RAID 5

          Thanks again. I may be able to convince them to get some additional drives, but it most likely won't be until the new year.

          Of the 35 only @ 10 users have light to moderate use. The rest are occasional. Will the server function properly, for now, as is?

          If I can convince them to add the drives in the New Year, can the transaction logs be easily moved without causing too much disruption?

          Thanks again for all your help.

          Comment


          • #6
            Re: Exchange Transaction Logs on RAID 5

            The server will function correctly - it is just data after all.
            If the RAID card can support two arrays, and you definitely think that you will extra drives in the new year, then I would probably configure two drives as a mirror, and have the third drive on its own.

            Take the mirrored array and partition it twice, 20gb and then the rest.

            Install Exchange on to the C drive in the default location.
            Put the databases on to the D: drive (second partition).
            Put the transaction logs on to the separate disk.

            When you are ready to introduce the additional disks, move the logs to the second partition where the database is.
            Add the spare drive to the RAID 5 array and move the database to the RAID 5 array. Leave the logs where they are.

            Moving logs and the database around isn't too much trouble. Where the problems come is changing the arrays, as you cannot change arrays on the fly - you have to erase the drives and reinstall.

            If there is even a possibility that the additional drives will not be supplied, then you will have to go with what you have and take the performance hit. Even after adding the extra drives you will not get optimium levels of performance.

            If you get it right now, you will not have to touch the server again for quite some time.

            Simon.
            --
            Simon Butler
            Exchange MVP

            Blog: http://blog.sembee.co.uk/
            More Exchange Content: http://exchange.sembee.info/
            Exchange Resources List: http://exbpa.com/
            In the UK? Hire me: http://www.sembee.co.uk/

            Sembee is a registered trademark, used here with permission.

            Comment


            • #7
              Re: Exchange Transaction Logs on RAID 5

              >>Even after adding the extra drives you will not get optimium levels of performance. <<


              Thanks again, I suppose there is a possibility that the client might find the performance "as is" adequate and opt not to add the addition drives in the new year.

              The thinking was install everything on a 80gb partition seperate from the OS. Then, if they want to move the transaction logs just add 2 more drives and mirror them. Then just move the log location to the new drives.

              Will this help with the performance?


              Thanks again for all your help, I understand the "optimal" configuration recommendations. They just have a limited budget and I wanted to be able to use what they had, if possible.

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