Re: Allocation strategy - dynamic zone for small files

[Andreas Dilger <adilger@clusterfs.com>]

On Nov 14, 2006  14:41 +0100, Ihar `Philips` Filipau wrote:
> More I'm thinking about that, more I'm convinced that some sort of
> compromise is required. E.g. file system with 2/more cluster sizes:
> for example 4k for small/medium files, 64+k cluster for large files.
> Files of 100+MB sizes are not that rare anymore (home video/audio
> processing now is affordable as never before). But on other side tiny
> files like e.g. found in /etc or ~/.kde/* are not going to disappear
> anytime soon.

Well, current plan is that new allocator (mballoc + delalloc) from
Alex Tomas will do efficient in-memory allocation of many contiguous
blocks, and extents format will allow efficient on-disk storage of
many contiguous blocks, so benefit of larger cluster size in disk
format is minimal.

Essentially, delaying the disk allocation until a file is large/complete
(delalloc) and then using a buddy allocator in memory to get contiguous
chunks of disk is better than hard 64K+ cluster because it avoids
internal fragmentation and allows much more optimal/efficient placement
than just a factor of 16 reduction in the block count.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.