> From: Bob Friesenhahn [mailto:bfrie...@simple.dallas.tx.us] > Sent: Tuesday, December 28, 2010 9:23 PM > > > 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.
Nope. I'm not confused at all. I'm making a distinction between "short stroking" and "advanced short stroking." Where simple "short stroking" does as you said - eliminates the head seek time but still susceptible to rotational latency. As you said, the ZIL already effectively accomplishes that end result, provided a dedicated spindle disk for log device, but does not do that if your ZIL is on the pool storage. And what I'm calling "advanced short stroking" are techniques that effectively eliminate, or minimize both seek & latency, to zero or near-zero. What I'm calling "advanced short stroking" doesn't exist as far as I know, but is theoretically possible through either special disk hardware or special drivers. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
