Re: tools to improve harddisk performance by short-stroking?

[Zhang Weiwu <zhangweiwu@realss.com>]

On 2010年10月08日 04:03, Ron Johnson wrote:
>
> You'd need to add accounting complexity to the kernel (where would it
> put the accounting data?)

I had been too brief, but if you read the article I referred to, it
works best only in case you put rarely accessed file to the posterior,
not 'infrequently accessed file' to the posterior.

To find out infrequently accessed file you need accounting. To find
rarely accessed file you only need to look at atime. The difference is
due to there are two factors slows down: disk spinning speed and head
movement speed. If there is only the disk spin speed factor, then put
infrequent file to the bottom helps a lot; if counting in the second
factor, than only putting rarely accessed files at the bottom helps a
lot. Suppose you have one infrequently accessed file at the posterior,
and it's accessed, than the moment accessing it, access to every other
file slows down as the head have to travel back afterwards, that's why
the article suggest not to put any data at all to the posterior (even
infrequent ones), while I think not putting any data at the posterior
should have the same performance gain of putting only rarely accessed
file there.