Sample layouts for a server database on DS5000 series disks

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Samples illustrate several ways to follow configuration guidelines for the server database when you use DS5000 series Fibre Channel disks. The samples illustrate advantages and disadvantages of configuration choices.

Remember: Ensure that the server database, recovery logs, and storage pools are on different disks.

Sample 1: Good layout for a small server

By using five disks for the database, you can set up the disks with the following characteristics. See Figure 1.
  • Configure disks in a 4 + 1 RAID 5 array.
  • Set the stripe size to 256 KB.
  • Define one directory (also called a container) and one logical volume for the database.
  • Set the DB2_Parallel_IO environment variable: 
    DB2_Parallel_IO=*:4
    The IBM Db2 program that is the server's database manager uses this value when it balances load across the disks.
Figure 1. Database layout for a small server
Five disks are in a 4 + 1 RAID 5 array. One logical volume spans across all five disks. The one logical volume contains the database directory.
This layout has the following advantages:
  • The layout follows the guidelines for optimal stripe size.
  • The layout follows the guidelines for having a one-to-one correspondence between logical volumes and containers.
The layout has the following disadvantages:
  • Write operations for parity bits can affect performance if the system has a small cache.
  • The layout has only one container for the database, which is typically not optimal but might not be a problem for small server workloads.
  • Database and database indexes are spread across only five disks.

Sample 2: Better layout that uses RAID 10

By using eight disks for the database, you can set up the disks with the following characteristics. See Figure 2.
  • Configure disks in a 4 + 4 RAID 10 array.
  • Set the stripe size to 256 KB.
  • Define one directory (also called a container) and one logical volume for the database.
  • Set the DB2_Parallel_IO environment variable: 
    DB2_Parallel_IO=*:4
Figure 2. Database layout that uses eight disks in a RAID 10 array
Eight disks are in a 4 + 4 RAID 10 array. One logical volume spans across four disks, and is mirrored on the additional four disks. The one logical volume contains the database directory.
This layout has the following advantages:
  • The layout follows the guidelines for optimal stripe size.
  • The layout follows the guidelines for having a one-to-one correspondence between logical volumes and containers.
  • The system does not have the performance cost of parity write operations.
  • RAID 10 is an optimal choice for the server database. With its two sets of disks, this configuration results in faster reads for the database.
The layout has the following disadvantages:
  • The layout has only one container for the database, which is typically not optimal but might not be a problem for small server workloads.
  • The layout requires twice as many disks as in sample 1 because of the use of RAID 10 instead of RAID 5.

Sample 3: Better layout that uses RAID 10 and more containers

By using 16 disks for the database, you can set up the disks with the following characteristics. See Figure 3.
  • Configure the disks in two 4 + 4 RAID 10 arrays.
  • Set the stripe size to 256 KB.
  • Define two directories (also called containers) and two logical volumes for the database.
  • Set the DB2_Parallel_IO environment variable: 
    DB2_Parallel_IO=*:4
Figure 3. Database layout that uses 16 disks in two RAID 10 arrays
The 16 disks are in two 4 + 4 RAID 10 arrays. For each array, one logical volume spans across four disks, and is mirrored on the additional four disks. The one logical volume contains a database directory.
This layout has the following advantages:
  • The layout follows the guidelines for optimal stripe size.
  • The layout follows the guidelines for having a one-to-one correspondence between logical volumes and containers.
  • The system does not have the performance cost of parity write operations.
  • RAID 10 is an optimal choice for the server database. With its two sets of disks, this configuration results in faster reads for the database.
  • Many more physical spindles means better performance for database read and write operations.
  • More database containers means that more data can be prefetched by the Db2 software.
The disadvantage is that this layout requires more disks than the other samples.