On Mon, Dec 27, 2010 at 09:06:45PM -0500, Edward Ned Harvey wrote: > > From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > > boun...@opensolaris.org] On Behalf Of Nicolas Williams > > > > > Actually I'd say that latency has a direct relationship to IOPS because > it's the > > time it takes to perform an IO that determines how many IOs Per Second > > that can be performed. > > > > Assuming you have enough synchronous writes and that you can organize > > them so as to keep the drive at max sustained sequential write > > bandwidth, then IOPS == bandwidth / logical I/O size. Latency doesn't > > 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.
Clearly the application cares about _synchronous_ operations that are meaningful to it. In the case of an NFS application that would be open() with O_CREAT (and particularly O_EXCL), close(), fsync() and so on. For a POSIX (but not NFS) application the number of synchronous operations is smaller. The rate of asynchronous operations is less important to the application because those are subject to caching, thus less predictable. But to the filesystem the IOPS are not just about synchronous I/O but about how many distinct I/O operations can be completed per unit of time. I tried to keep this clear; sorry for any confusion. Nico -- _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
