is this a direct write to a zfs filesystem or is it some kind of zvol export?
anyway, sounds similar to this: http://opensolaris.org/jive/thread.jspa?threadID=105702&tstart=0 On Tue, Jun 23, 2009 at 7:14 PM, Bob Friesenhahn<bfrie...@simple.dallas.tx.us> wrote: > It has been quite some time (about a year) since I did testing of batch > processing with my software (GraphicsMagick). In between time, ZFS added > write-throttling. I am using Solaris 10 with kernel 141415-03. > > Quite a while back I complained that ZFS was periodically stalling the > writing process (which UFS did not do). The ZFS write-throttling feature > was supposed to avoid that. In my testing today I am still seeing ZFS stall > the writing process periodically. When the process is stalled, there is a > burst of disk activity, a burst of context switching, and total CPU use > drops to almost zero. Zpool iostat says that read bandwidth is 15.8M and > write bandwidth is 15.8M over a 60 second averaging interval. Since my > drive array is good for writing over 250MB/second, this is a very small > write load and the array is loafing. > > My program uses the simple read->process->write approach. Each file written > (about 8MB/file) is written contiguously and written just once. Data is > read and written in 128K blocks. For this application there is no value > obtained by caching the file just written. From what I am seeing, reading > occurs as needed, but writes are being batched up until the next ZFS > synchronization cycle. During the ZFS synchronization cycle it seems that > processes are blocked from writing. Since my system has a lot of memory and > the ARC is capped at 10GB, quite a lot of data can be queued up to be > written. The ARC is currently running at its limit of 10GB. > > If I tell my software to invoke fsync() before closing each written file, > then the stall goes away, but the program then needs to block so there is > less beneficial use of the CPU. > > If this application stall annoys me, I am sure that it would really annoy a > user with mission-critical work which needs to get done on a uniform basis. > > If I run this little script then the application runs more smoothly but I > see evidence of many shorter stalls: > > while true > do > sleep 3 > sync > done > > Is there a solution in the works for this problem? > > Bob > -- > Bob Friesenhahn > bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ > GraphicsMagick Maintainer, http://www.GraphicsMagick.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
