> From: Roy Sigurd Karlsbakk [mailto:r...@karlsbakk.net] > > > Bear a few things in mind: > > > > iops is not iops. > <snip/> > > I am totally aware of these differences, but it seems some people think > RAIDz is nonsense unless you don't need speed at all. My testing shows (so > far) that the speed is quite good, far better than single drives.
There is a grain of truth. For sequential IO, either reads or writes, raidz will be much faster than a single drive. For random IO, it's more complex... If you're doing random writes, then ZFS will make them into sequential IO, and hence, your raidz will greatly outperform a single drive. If you're doing random reads, you will get the performance of a single drive, at best. In order to test random reads, you have to configure iozone to use a data set which is much larger than physical ram. Since iozone will write a big file and then immediately afterward, start reading it ... It means that whole file will be in cache unless that whole file is much larger than physical ram. You'll get false read results which are unnaturally high. For this reason, when I'm using an iozone benchmark, I remove as much ram from the system as possible. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
