scsi properties

[vietkangta]

what does tagged queue and synchronous transfers do for the hardrive? i tried googling it but cant find any sites with an easy to understand definition.

 

[UICompE02]

Tagged queueing allows the controller to send multiple requests to a hard disk and allow the hard disk to complete the outstanding requests in the order it can best service them. (since the hard drive knows where data is physically located, the firmware on the drive can then determine the best order to service the requests to get the best performance). This provides the most benefit in a multi-user environment where requests are coming from multiple applications for data that is stored in different areas across the disk.

Synchronous transfers mean that the data transfers are tied to a clock that is provided on the SCSI bus. This is in contrast to Asynchronous transfers that require a Request and Acknowledge for each chunk of data that is transferred. Basically, with SCSI, any of the modern high-speed modes will run Synchronously for performance reasons. Async modes are typically very slow and only remain as an option for backward compatibility reasons.

 

[vietkangta]

oh thansk a lot