Administrator Guide : Performance tuning : Tuning I/O : Distributing I/O
  
Distributing I/O
Disk contention occurs when multiple processes try to access the same disk simultaneously. To avoid contention, move files from heavily accessed disks to less active disks until they all have roughly the same amount of I/O.
Follow these guidelines:
Use a separate disk for log files.
Divide your database into several files and place each of these database files on a separate disk. See Configuring solidDB® for more details.
Consider using a separate disk for the external sorter
Typically it is faster to scan a table if the disk file is contiguous on the disk rather than spread across many non-contiguous disk blocks. To reduce existing fragmentation, you might want to run defragmentation software if one is available on your system. If your database file is growing, you might be able to reduce future file fragmentation by using the configuration parameter IndexFile.ExtendIncrement. Increasing the size of this parameter tells the server to allocate larger amounts of disk space when it runs out of space. Increasing the value does not guarantee contiguity because the operating system itself can allocate non-contiguous sectors to satisfy even a single request for more space. As a general rule, larger values of IndexFile.ExtendIncrement improve performance slightly, while smaller values keep the database size slightly smaller.
See also
Tuning I/O