Caching Parameters

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This section controls allows you to control the read and write caching parameters saved within the drive. It is important to note several aspects of this which are:
·If you change a current value, then your drive will be reconfigured as soon as you press the update button. When power is recycled to your disk drives, they will revert to the default values.  
·If you change the default value, then the drive will initialize to those settings at power-up.  
·Factory values are displayed so you know how the drive is configured from the factory. They are not necessarily the best settings to use on your system. It is also possible that a device driver, another software product, you system supplier, or somebody also changed the default values.  
·When SMARTMon is invoked, it will read the cache settings you used from the registry, and reconfigure the disk  
·Not all drives allow all fields to be modified.  
·Don't change these values without understanding the consequences. In order to understand how your system might be affected by changing them, please consult your drive vendor.  
·All of these fields are associated with SCSI Mode Page 8, and checked fields indicate the corresponding bit is set to one. s always, enable write cache at your own risk. In the event of a power failure, (or most probably the blue-screen-of-death) than data may be lost.  

Fields and their values include:
·Cache Segments Controlled by Initiator: The device will use the number of cache segments or cache segment size fields to control the cache segmentation. When this field is unchecked, the caching is controlled by the disk drive. When checked, the initiator (i.e., SCSI controller) sends this information. This setting corresponds to the value of the IC bit.  
·Device Aborts Pre-Fetch Upon Selection: When unchecked, the termination of any active pre-fetch is defendant upon the values of the four pre-fetch fields on this screen. When checked, the target aborts pre-fetch upon selection. This setting corresponds to the ABPF bit.  
·Device Performs Caching Analysis: When checked, the target performs caching analysis during subsequent operations. When unchecked, the caching analysis will be disabled to reduce overhead time or to prevent non pertinent operations from impacting tuning values. (Note, caching-related log parameters will be maintained due to the negligible effects of updating them when this function is disabled). This setting corresponds to the CAP bit.  
·Pre-Fetch Across Time Discontinuties: This field, also known as the Discontinuity (DISC bit)when checked, requests that the target continue the pre-fetch across time discontinuities, such as across cylinders and tracks, up to the limits of the space available for pre-fetch. When unchecked, the DISC requests that the pre-fetches be truncated (or wrapped) at time discontinuities. Even though the target supports initiators setting DISC=0, pre-fetches across track boundaries may be executed dependent upon other prefetch mode parameters when DISC is set to 0.  
·Cache Segment Size Controls Caching Segmentation: This field, when set to one (checked), indicates that the Cache Segment Size is to be used to control caching segmentation. When SIZE = 0, the initiator requests that the Number of Cache Segments is to be used to control caching segmentation. The exception to this is when IC = 0. In that case the target determines cache segmentation. This field corresponds to the SIZE bit.  
·Write Cache Enabled: A WCE (Write Cache Enable) bit of 0 specifies that the target returns Good Status for a write command only after successfully writing all of the data to the medium. The WCE bit of 1 specifies that the target may return Good Status for a write command after successfully receiving the data but before writing to the medium.  
·(Multiplication Factor) Pre-Fetch Parameters are Multiplied by Number of Blocks Requested in Reads: This bit determines how the Maximum and Minimum Pre-fetch parameters are interpreted. If this bit = 0, the parameters are used as-is. If the bit is equal to 1, the parameters are multiplied by the number of blocks requested in the read command. This corresponds to the MF bit.  
·Read Cache Enabled: If checked, the target may return all or part of the data requested by a read command by accessing the drive's data buffer, not the media. Note - this corresponds to the opposite value of the RCD bit, which means read cache disable (RCD bit).  

The next four fields, also with factory and current columns may have any value from 0 to 65535, and have the following legends and meanings:
·Prevent read-ahead after reads longer than these # of blocks: Defined as the Disable Pre-fetch Transfer Length, is used to prevent read-ahead after read commands that are longer than the specified number of blocks. If the parameter is set to 0, a read-ahead is not performed.  
·Min # of blocks for read-ahead: Defined as the minimum pre-fetch, is used to set a lower limit on the number of blocks to read-ahead after a read command. The value of 0 indicates that pre-fetching is terminated whenever another command is ready for executing. A value in the rage 1-65534 is the number of blocks prefetched following a read operation that will not be preempted by a subsequent command. The actual number of blocks prefetched without interruption may be decreased by other reasons such as space in the cache segment, maximum prefetch, and the end of the media. The value of 65535 indicates that the drive self-adapts the maximum pre-fetch value. The adaptive minimum prefetch algorithm uses the detected workload seen by the drive to optimize throughput and response time for that workload.  
·Max # of blocks for read-ahead: Defined as the maximum pre-fetch, is used to set an upper limit on the number of blocks to read-ahead after a read command. Other factors, such as segment size, drive size, retention priorities, commands in the queue, and new commands may also limit the read-ahead.  
·If Multiplication factor enabled, limit read-ahead to this # of blocks: This field, also known as the Maximum Pre-Fetch Ceiling, limits the read-ahead just like maximum pre-fetch does when the MF bit is set to 0. But when the MF bit is set to 1, it also limits the read ahead to an absolute value, unlike maximum prefetch which uses a value scaled by the transfer length when MF = 1.  

Press UPDATE to record the changes in the drive, as well as the registry. By doing so, S.M.A.R.T. Disk Monitor will automatically program your disk drive to use these settings when the program is invoked.

Finally, some drives, particularly the high-end IBM drives have additional cache-related fields. They are not reported in this program.