iSCSI attached server performance

For iSCSI attached servers, there are multiple configuration options to adjust for better performance capacity as needed. Some options may require different target disk configurations or volumes on the integrated servers.

Windows disk configuration

For iSCSI attached integrated servers, the virtual disk drives are optimized for:

• 1 disk partition per virtual drive.
• 1 gigabyte or larger storage spaces.
• NTFS file system formatted with 4 kilobyte or larger cluster sizes.

These guidelines allow the iSeries™ to efficiently manage the storage space memory, improving the disk performance. These guidelines also affect IXS and IXA attached servers, but to a much smaller degree.

If you use the Change Network Storage Space (CHGNWSSTG) CL command to increase a storage space size, be sure to use the Windows Server 2003 DISKPART command to also increase the size of the partition on Windows.

iSeries memory pools

For iSCSI attached servers, the storage operations occur through an iSeries memory pool. This memory essentially acts as a cache to the disk operations, so the size of the memory can affect the Windows disk performance. This I/O does not directly cause page faulting in the base pool. However, since pool memory is shared with other i5/OS™ applications, Windows disk operations may cause page faulting in other applications, or other applications may induce paging of iSCSI disk operations. In extreme cases, you may need to adjust memory pool sizes or assign applications to other memory pools to mitigate memory problems.

IXS and IXA attached servers do not perform disk operations through a base memory pool. They use reserved memory within the machine pool (System Pool ID 1). Thus, the disk operations do not share memory with other applications.

iSCSI performance configurations

On iSCSI attached integrated servers, if a single network fabric is reaching capacity, you can add channels with additional iSCSI HBAs in both the xSeries® and iSeries servers (assuming the interconnecting network also has available bandwidth).

There are several ways that you can spread the iSCSI and network traffic between the separate channels:

• Dedicate SCSI operations to one channel, and virtual Ethernet operations to another.
• Use two storage targets. Each target should be linked to a separate HBA paths. See Manage iSCSI host bus adapters.
  • On Windows, direct applications to use both drives (if possible), or dedicate the drives to different applications to spread the total disk operations between the drives.
  • Configure the two disks in a Windows dynamic volume set with the data striped across the two drives. As applications use the volume, the disk operations will automatically balance across the drives in the volume set.