> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Edward Ned Harvey > > Ok, what we've hit here is two people using the same word to talk about > different things. Apples to oranges, as it were. Both meanings of "IOPS" > are ok, but context is everything. > > There are drive random IOPS, which is dependent on latency and seek time, > and there is also measured random IOPS above the filesystem layer, which is > not always related to latency or seek time, as described above.
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.) If using ZFS for AFP (and consequently BDB)... If you disable the ZIL you will have maximum performance, but maybe you're not comfortable with that because you're not convinced of stability with ZIL disabled, or for other reasons. * If you put your BDB or ZIL on a spindle dedicated device, it will perform better than having no dedicated device, but the difference might be anything from 1x to 10x, depending on where your bottlenecks are. AKA no improvement is guaranteed, but probably you get at least a little bit. * If you put your BDB or ZIL on a SSD dedicated log device, it will perform still better, and again, the difference could be anywhere from 1x to 10x depending on your bottlenecks. * If you disable your ZIL, it will perform still better, and again, the difference could be anywhere from 1x to 10x. Realistically, at some point you'll hit a network bottleneck, and you won't notice the improved performance. If you're just doing small numbers of large files, none of the above will probably be noticeable, because in that case latency is pretty much irrelevant. But assuming you have at least a bunch of reasonably small files, IMHO that threshold is at the SSD, because the latency of the SSD is insignificant compared to the latency of the network. But even with short-stroking getting the latency down to 2ms, that's still significant compared to network latency, so there's probably still room for improvement over the short-stroking techniques. At least, until somebody creates a more advanced short-stroking which gets latency down to near-zero, if that will ever happen. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
