Tony Galway writes: > Let me elaborate slightly on the reason I ask these questions. > > I am performing some simple benchmarking, and during this a file is > created by sequentially writing 64k blocks until the 100Gb file is > created. I am seeing, and this is the exact same as VxFS, large pauses > while the system reclaims the memory that it has consumed. > > I assume that since ZFS (back to the write cache question) is > copy-on-write and is not write caching anything (correct me if I am > wrong), it is instead using memory for my read-cache. Also, since I > have 32Gb of memory the reclaim periods are quite long while it frees > this memory - basically rendering my volume unusable until that memory > is reclaimed. > > With VxFS I was able to tune the file system with write_throttle, and > this allowed me to find a balance basically whereby the system writes > crazy fast, and then reclaims memory, and repeats that cycle. > > I guess I could modify c_max in the kernel, to provide the same type > of result, but this is not a supported tuning practice - and thus I do > not want to do that. > > I am simply trying to determine where ZFS is different, the same, and > where how I can modify its default behaviours (or if I ever will). > > Also, FYI, I'm testing on Solaris 10 11/06 (All testing must be > performed in production versions of Solaris) but if there are changes > in Nevada that will show me different results, I would be interested > in those as an aside. >
Today, a txg sync can take a very long time for this type of workload. A first goal of write throttling will be to at least bound the sync times. The amount of dirty memory (not quickly reclaimable) will then be limited and ARC should be much better at adjusting itself. A second goal will be to keep sync times close to 5 seconds further limiting the RAM consumption. > > This message posted from opensolaris.org > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
