Its a starting point anyway. The key is to try and draw useful conclusions from the info to answer the torrent of "why is my ARC 30GB???"
There are several things I'm unclear on whether or not I'm properly interpreting such as: * As you state, the anon pages. Even the comment in code is, to me anyway, a little vague. I include them because otherwise you look at the hit counters and wonder where a large chunk of them went. * Prefetch... I want to use the Prefetch Data hit ratio as a judgment call on the efficiency of prefetch. If the value is very low it might be best to turn it off..... but I'd like to hear that from someone else before I go saying that. In high latency environments, such as ZFS on iSCSI, prefetch can either significantly help or hurt, determining which is difficult without some type of metric as as above. * There are several instances (based on dtracing) in which the ARC is bypassed... for ZIL I understand, in some other cases I need to spend more time analyzing the DMU (dbuf_*) for why. * In answering the "Is having a 30GB ARC good?" question, I want to say that if MFU is >60% of ARC, and if the hits are mostly MFU that you are deriving significant benefit from your large ARC.... but on a system with a 2GB ARC or a 30GB ARC the overall hit ratio tends to be 99%. Which is nuts, and tends to reinforce a misinterpretation of anon hits. The only way I'm seeing to _really_ understand ARC's efficiency is to look at the overall number of reads and then how many are intercepted by ARC and how many actually made it to disk... and why (prefetch or demand). This is tricky to implement via kstats because you have to pick out and monitor the zpool disks themselves. I've spent a lot of time in this code (arc.c) and still have a lot of questions. I really wish there was an "Advanced ZFS Internals" talk coming up; I simply can't keep spending so much time on this. Feedback from PAE or other tuning experts is welcome and appreciated. :) benr. This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
