On Tue, 28 Dec 2010, Edward Ned Harvey wrote:
In any event, the relevant points are: The question of IOPS here is relevant to conversation because of ZIL dedicated log. If you have advanced short-stroking to get the write latency of a log device down to zero, then it can compete against SSD for purposes of a log device, but nobody seems to believe such technology currently exists, and it certainly couldn't compete against SSD for random reads. (ZIL log is the only situation I know of, where write performance of a drive matters and read performance does not matter.)
It seems that you may be confused. For the ZIL the drive's rotational latency (based on RPM) is the dominating factor and not the lateral head seek time on the media. In this case, the "short-stroking" you are talking about does not help any. The ZIL is already effectively "short-stroking" since it writes in order.
The (possibly) worthy optimizations I have heard about are writing the log data in a different pattern on disk (via a special device driver) with the goal that when when drive sync request comes in the drive is quite likely to be able to write immediately. Since such optimizations are quite device and write-load dependent, it is not worth while for a large company to develop the feature (but would make for an interesting project).
Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, 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
