How can I improve I/O performance?

A. If your system is fairly I/O intensive, you may benefit from raising the I/O Page Lock Limit, which can increase the effective rate the OS reads or writes data to the hard disks.

First, benchmark your common tasks. See how long it takes to load and save large files, how long it takes to search a database or run a common program; just do your normal tasks, timing them to record how fast they are. Then follow these steps:

  1. Start the registry editor (regedit.exe)
  2. Move to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management
  3. Double click IoPageLockLimit
  4. Enter a new value.
    This value is the maximum bytes you can lock for I/O operations. A value of 0 defaults to 512KB. Raise this value by 512KB increments (enter "512", "1024", etc.), then exit regedit.exe and benchmark your system after each adjustment. When an increase does not give you a significant performance boost, go back and undo the last increment.
    Caution: There is a limit to this. Do not set this value (in bytes) beyond the number of megabytes of RAM times 128. That is, if you have 16 MB RAM, do not set IoPageLockLimit over 2048 bytes; for 32MB RAM, do not exceed 4096 bytes, and so on.
    Click OK.
  5. Close the registry editor

Unless you do little I/O, this should give you a significant boost in performance.

I have recently learned that this value specifies the maximum amount of application memory that can be locked into physical memory at any given point in time. Device drivers typically lock user buffers in order to transmit them to a hardware device. If the limit is exceeded an I/O operation will simply return a STATUS_QUOTA_EXCEEDED error to the application. Thus, the value should only be raised if I/O operations begin returning this error, and it has absolutely no effect on performance.

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