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SubjectRe: Large disk partition over 300GB
Gotta disagree somewhat ... yes time vs space :)
The logic was right and not quite 10 years...

I remember back in '95 on Solaris 2.5.1 oops, yes, Solaris
that it supported at least in some fragment reallocation
function the support for time vs space based on a minfree
value...This is/was ufs code.

Ask your Sun buddies to check the Solaris 8 code, would
not doubt that it is still there..

I haven't looked at ext2 code.

Mitch
PS: Got one for you, what does ABR mean? Hint it is a QoS
ATM term...
=======

Stephen C. Tweedie wrote:
>
> Hi,
>
> On Wed, 14 Jul 1999 22:16:18 -0700, merblich <merblich@gateway.net>
> said:
>
> > Normally, a file system will allocate disk blocks based on a time
> > vs space algorithm. By having blocks free in a number of locations,
> > the best location to allocate the disk block due to the growing
> > of fragments or just a new block can be realized. A couple of factors
> > in determining this is interleave, rotation speed, time to seek, etc.
>
> Not any more. That used to be the space, nobody makes drives like that
> any more. For the last ten years there have been large numbers of
> pipeline stages added into the disk IO path, from track buffers to
> on-disk caches to asynchronous scsi tagged commands to operating system
> readahead buffers. The _only_ things you can effectively optimise for
> when allocating data are (a) sequential access, and (b) approximate
> proximity of related data. Effective explicit data placement just
> cannot be done by the OS any more, and ext2 (being less than ten years
> old) has never tried to do so.
>
> > Once the file system's free space decreases to a specified point, the
> > allocation then just allocates blocks due to their availability. My
> > guess, is that 5% is the point where this tradeoff is made.
>
> Not at all. Ext2 always uses the same algorithm. It just becomes less
> effective if there is less free space. The exact rate at which things
> fall off obviously depends on the access patterns, which is one reason
> why the reserved space region is configurable.
>
> --Stephen

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