On 11 January, 2007 - Mark Maybee sent me these 4,7K bytes: > >It would seem, from reading between the lines of previous emails, > >particularly the ones you've (Mark M) written, that there is a rule of > >thumb that would apply given a standard or modified ncsize tunable?? > > > >I'm primarily interested in a calculation that would allow settings that > >would reduce the possibility of the machine descending into "swap hell". > > > Ideally, there would be no need for any tunables; ZFS would always "do > the right thing". This is our grail. In the meantime, I can give some > recommendations, but there is no "rule of thumb" that is going to work > in all circumstances. > > ncsize: As I have mentioned previously, there are overheads > associated with caching "vnode data" in ZFS. While > the physical on-disk data for a znode is only 512bytes, > the related in-core cost is significantly higher. > Roughly, you can expect that each ZFS vnode held in > the DNLC will cost about 3K of kernel memory. > > So, you need to set ncsize appropriately for how much > memory you are willing to devote to it. 500,000 entries > is going to cost you 1.5GB of memory.
Due to fragmentation, 200k entries can eat over 1.5GB memory too. http://www.acc.umu.se/~stric/tmp/dnlc-plot2.png This is only dnlc-related buffers on a 2GB machine.. the spike at the end caused the machine to more or less stand still. > zfs_arc_max: This is the maximum amount of memory you want the > ARC to be able to use. Note that the ARC won't > necessarily use this much memory: if other applications > need memory, the ARC will shrink to accommodate. > Although, also note that the ARC *can't* shrink if all > of its memory is held. For example, data in the DNLC > cannot be evicted from the ARC, so this data must first > be evicted from the DNLC before the ARC can free up > space (this is why it is dangerous to turn off the ARCs > ability to evict vnodes from the DNLC). I've tried that.. didn't work out too great due to fragmentation.. Left non-kernel with like 4MB to play with.. /Tomas -- Tomas Ögren, [EMAIL PROTECTED], http://www.acc.umu.se/~stric/ |- Student at Computing Science, University of Umeå `- Sysadmin at {cs,acc}.umu.se _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
