Clarence wrote:
>Well SURE. To me, you are saying just what *I* said. That was a LARGE
>file, you were reading it for the first time essentially, because you
>were reading only a small amount (your readahead size) at a time, and
>of course I don't know the extent of your fragmentation, but you must
>agree that if your disk was badly fragmented most of the readahead data
>is useless ?
Since I had created the file before using it (with a restart in betwen of
course) I had *no* fragmentation on the file.
And it's my oppinion that even if it was fragmented I would still gain very
much from read-ahead (IMHO same or even more). The test I did was so absurd
so we can't count it of course, but it's my belief that the cache will read
ahead in the file - not on the disk. The cache on the HD (an unknown
ammount for me) probably work diffrently. Even if you are correct about
read-ahead you would still gain from it since you can't have the worst case
scenario (1 allocated unit here, another in the other part of the HD and
then the third somewhere else and so on).
>I DO agree that when readahead CAN do any good, it does a LOT of good.
>I just don't think it does any good MOST of the time, and on most HDs,
>(fragmented) it does harm. ;-)
Most HDs (among us anyway) aren't fragmented IMHO. I don't know about you
but I use defrag/f on my drives on a regular basis (but I set the BATch
file up so it doesn't use defrag if nothing has changed since the last time
thereby saving some time).
//Bernie
