On Wed, 19 Mar 2008, Bill Moloney wrote: > When application IO sizes get small, the overhead in ZFS goes > up dramatically.
Thanks for the feedback. However, from what I have observed, it is not a full story at all. On my own system, when a new file is written, the write block size does not make a significant difference to the write speed. Similarly, read block size does not make a significant difference to the sequential read speed. I do see a large difference in rates when an existing file is updated sequentially. There is a many orders of magnitude difference for random I/O type updates. I think that there some rather obvious reasons for the difference between writing a new file, or updating an existing file. When writing a new file, the system can buffer up to a disk block's worth of size prior to issuing a a disk I/O, or it can immedialy write what it has and since the write is sequential, it does not need to re-read prior to write (but there may be more metadata I/Os). For the case of updating part of a disk block, there needs to be a read prior to write if the block is not cached in RAM. If the system is short on RAM, it may be that ZFS issues many more write I/Os than if it has a lot of RAM. Bob ====================================== Bob Friesenhahn [EMAIL PROTECTED], http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
