sequential disk read speed
From: Darren <anon5874_at_yahoo.com>
Date: Wed, 20 Aug 2008 17:36:41 -0700 (PDT)
Message-ID: <26ec87ba-28f8-44c2-88fb-a6c7f588f100_at_26g2000hsk.googlegroups.com>
I am learning about database systems, and I am reading a book called "Physical Database Design".
Date: Wed, 20 Aug 2008 17:36:41 -0700 (PDT)
Message-ID: <26ec87ba-28f8-44c2-88fb-a6c7f588f100_at_26g2000hsk.googlegroups.com>
I am learning about database systems, and I am reading a book called "Physical Database Design".
It gets to a bit about a large sequential access (e.g. for a full table scan), and does the following:
It says "Since most disk systems use prefetch buffers to speed up
table scans, we
assume a 64 KB prefetch block"
So to calculate the time for a full table scan, it multiples the number of 64KB blocks by the time it takes to seek and read (2.02ms). In other words, it is seeking each 64KB block.
Why can a disk only read 64KB at a time? Is this a valid assumption?
Is this a disk limitation or a file system limitation?Thanks Received on Thu Aug 21 2008 - 02:36:41 CEST