On Tue, Sep 18, 2007 at 11:00:40AM +0100, Mel Gorman wrote: > We still lack data on what sort of workloads really benefit from large > blocks (assuming there are any that cannot also be solved by improving > order-0). No we don't. All workloads benefit from larger block sizes when you've got a btree tracking 20 million inodes and a create has to search that tree for a free inode. The tree gets much wider and hence we take fewer disk seeks to traverse the tree. Same for large directories, btree's tracking free space, etc - everything goes faster with a larger filesystem block size because we spent less time doing metadata I/O. And the other advantage is that sequential I/O speeds also tend to increase with larger block sizes. e.g. XFS on an Altix (16k pages) using 16k block size is about 20-25% faster on writes than 4k block size. See the graphs at the top of page 12: http://oss.sgi.com/projects/xfs/papers/ols2006/ols-2006-paper.pdf The benefits are really about scalability and with terabyte sized disks on the market..... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
