Adaptive Server 12.5 allows you to create and mount its database devices on raw bound devices for raw disk I/O. Raw disk I/O has performance advantages since it enables direct memory access from user address space to the physical sectors on the disk, omitting needless memory copy operations from the user address space to the kernel buffers.

Raw disk I/O also assumes that logical and physical I/O are simultaneous, and writes are guaranteed to flush to the disk when the system write() call returns.

For Red Hat 6.2 distributions, you must use a distribution with kernel 2.2.18, at minimum. Correct kernel errata packages can be downloaded from the Red Hat Web sitehttp://www.redhat.com.

When preparing a raw partition device, follow these guidelines:

To determine whether a device is a block device or a character device, run this command on the /dev/raw directory:

ls -l

“b” (block) or “c” (character) appears in the left-most column.

StepsChoosing a raw partition

  1. Determine which raw partitions are available.

  2. Determine the sizes of the raw partitions.

  3. From the list of available raw partitions, select a raw partition for each device, based on the size recommendations in Table 2-13.

  4. Verify with the operating system administrator that the partition you have chosen is available.

  5. Make sure the “sybase” user has read and write privileges to the raw partition.

    NoteFor more information on choosing a raw partition, see your operating system documentation.