On Tue, Apr 06, 2010 at 06:53:04PM -0700, Richard Elling wrote: > >> Disagree. Swap is a perfectly fine workload for SSDs. Under ZFS, > >> even more so. I'd really like to squash this rumour and thought we > >> were making progress on that front :-( Today, there are millions or > >> thousands of systems with deployed SSDs as boot and swap on a > >> wide variety of OSes. Go for it.
+1 > > Really? I'm generally not good for running swap on lower-performing > > SSDs over here in Java-land, but that may have to do with my specific > > workload. I'll take your word for it (of course, I'm voting for swap > > not being necessary on many machines these days). > > If you have to swap, you have no performance. Disagree. If you're thrashing heavily, yes. An SSD will make a difference in swap latency up until that point, but that won't help much when everything's stuck short for memory. However, a lot can happen before that point. Swapping out unused stuff (including idle services/processes and old tmpfs pages) can be very useful for performance, making room for the performance-sensitive working set. Some of your lower-priority processes can page in and out faster with an ssd, and smoothe the curve from memory pressure to total gridlock. Finally, this middle ground is where ssd root also helps, because executable text is paged from there. -- Dan.
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