Re: sequential disk read speed

From: David BL <>
Date: Fri, 22 Aug 2008 23:04:15 -0700 (PDT)
Message-ID: <>

On Aug 22, 10:13 pm, -CELKO- <> wrote:
> >> 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? <<
> The author has to provide some numbers to show how to calculate an
> estimation for disk access. Frankly, 64KB seems a little small for a
> modern computer other than a desktop machine.

Also on a desktop, 64k is too small. A desktop HD has higher seek +rotational delay and lower transfer rate giving about the same product as for an enterprise HD.

> What you might consider is the rise of solid state storage, which will
> start replacing moving disk hardware in the next few years. This with
> multi-core processors will change database design radically. We work
> in a trade where everything you know is wrong in five years :)

I wonder whether it will be less radical than might at first be imagined. CPU caches lead to significant variation in memory access times.

I few years ago I wrote a transient B+Tree and compared the performance to the STL map (a red black tree) that ships with MS Visual C++. I ran tests involving inserting a million randomly generated keys on a map keyed by 32 bit integers. The B+Tree was twice as fast at insertions and deletions, 35% faster at look up, and 10 times faster at iteration through the elements. Received on Sat Aug 23 2008 - 08:04:15 CEST

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