SQL Server Performance

SAN: useful to have different logical drives?

Discussion in 'SQL Server Clustering' started by Zirco, Jun 3, 2004.

  1. Zirco New Member

    Hi,

    I'm novice in clustering, please be lenient for dumbs questions.

    In a SQL2K Cluster using SAN as shared storage. The DBA creates drive X: for data and Y: for log. The idea is to have them separate for better performance.

    I am wondering if that could make any difference than just using a same logical drive. My reasonning is that the SAN unit is physically the same. The data channel through the same fiber cable. Whether we call drive X or Y, I have no idea how the SAN manages the storage internally.

    Question1: is there any benefit of using different SAN logical drives?

    Question2: is it OK to use the same SAN as shared quorum drive for the Windows 2000 Cluster?

    Thanks in advance for any help.
  2. satya Moderator

    1) Yes, there would be a benefit of using different logical drives or different resource groups.

    2) Cluster disk resources used by SQL Server should not be used for other cluster services (such as the quorum drive, file or printer shares, or Internet Information servers) unless the cluster has only one cluster disk resource. If you do use the SQL Server cluster disk for any of these resources, it may significantly affect your failover time and may also initiate failovers of SQL Server when no SQL Server problem exists.

    Satya SKJ
    Moderator
    http://www.SQL-Server-Performance.Com/forum
    This posting is provided “AS IS” with no rights for the sake of knowledge sharing.
  3. Zirco New Member

    quote:Originally posted by satya

    1) Yes, there would be a benefit of using different logical drives or different resource groups.

    2) Cluster disk resources used by SQL Server should not be used for other cluster services (such as the quorum drive, file or printer shares, or Internet Information servers) unless the cluster has only one cluster disk resource. If you do use the SQL Server cluster disk for any of these resources, it may significantly affect your failover time and may also initiate failovers of SQL Server when no SQL Server problem exists.

    What would you advise as shared storage device for #2?
  4. bradmcgehee New Member

    I can tell you what we are doing at our company, which may or may not apply to you.

    Our SAN device is an IBM ESS, and it used as our shared array for all of our clusters. We have chosen to put both log files and data files on the same logical drive for convenience, and because in our testing we did not see any significant difference in performance be separating them. On the other hand, we did create a separate logical drive for the quorum drive, which is also a strong recommendation from Microsoft.

    -----------------------------
    Brad M. McGehee, MVP
    Webmaster
    SQL-Server-Performance.Com
  5. Zirco New Member

    quote:Originally posted by bradmcgehee

    I can tell you what we are doing at our company, which may or may not apply to you.

    Our SAN device is an IBM ESS, and it used as our shared array for all of our clusters. We have chosen to put both log files and data files on the same logical drive for convenience, and because in our testing we did not see any significant difference in performance be separating them. On the other hand, we did create a separate logical drive for the quorum drive, which is also a strong recommendation from Microsoft.
    Thank you very much for your input. I assume that the quorum drive also uses the same SAN device. Please confirm. Is there any extra benefit for physically separating the quorum drive from the storage unit used by the data files? If yes, what kind of shared device?

    To be complete on the SAN part. Our SAN vendor told us that a shared RAID 0+1 has poor performance in clustering. It seems to me that the RAID array and the SAN are built using the same physical hard disks. I would like to know the reason of the difference in performance.

    In other words, for a failover SQL2K Cluster (2 nodes, active/active), would you recommend SAN over shared RAID 0+1?
  6. derrickleggett New Member

    Thank you very much for your input. I assume that the quorum drive also uses the same SAN device. Please confirm. Is there any extra benefit for physically separating the quorum drive from the storage unit used by the data files? If yes, what kind of shared device?

    It would just be another LUN on the same SAN device.

    To be complete on the SAN part. Our SAN vendor told us that a shared RAID 0+1 has poor performance in clustering. It seems to me that the RAID array and the SAN are built using the same physical hard disks. I would like to know the reason of the difference in performance.

    The difference in performance depends on vendor. Who are you looking at? What you really want to do is break the SAN environment into several RAID groups. You would have multiple RAID 10 arrays or RAID 5 arrays spread across the SAN. If you can afford it, you want the production environment to have seperate LUNs, each on their own RAID group for seperate log file, data file storage. This allows you to use multiple drives at the same time on the SAN and fully utilize the backplane.

    For other environments, you can spread multiple LUNs across the same RAID group. It allows you to carve space out of multiple RAID groups for a LUN and spread your disk IO out also.

    In other words, for a failover SQL2K Cluster (2 nodes, active/active), would you recommend SAN over shared RAID 0+1?

    It's not recommending one over another. If you have an active/active cluster, you will need a minimum of two arrays plus the quorum drive. On the SAN, you can consolidate all this in one storage device. You will still need the arrays though.

    Also, I don't like RAID 0+1. Stick to RAID 1, 10, and 5.

    MeanOldDBA
    derrickleggett@hotmail.com

    When life gives you a lemon, fire the DBA.
  7. Zirco New Member

    Hi Derrick,

    Thanks for your helpful info.

    >I don't like RAID 0+1

    By RAID 0+1 I meant stripping + mirroring by the Raid controler. Is it the same thing than RAID 10?

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