On Jun 24, 2011, at 5:29 AM, Sašo Kiselkov wrote: > Hi All, > > I'd like to ask about whether there is a method to enforce a certain txg > commit frequency on ZFS. I'm doing a large amount of video streaming > from a storage pool while also slowly continuously writing a constant > volume of data to it (using a normal file descriptor, *not* in O_SYNC). > When reading volume goes over a certain threshold (and average pool load > over ~50%), ZFS thinks it's running out of steam on the storage pool and > starts committing transactions more often which results in even greater > load on the pool. This leads to a sudden spike in I/O utilization on the > pool in roughly the following method: > > # streaming clients pool load [%] > 15 8% > 20 11% > 40 22% > 60 33% > 80 44% > --- around here txg timeouts start to shorten --- > 85 60% > 90 70% > 95 85%
What is a "pool load"? We expect 100% utilization during the txg commit, anything else is a waste. I suspect that you actually want more, smaller commits to spread the load more evenly. This is easy to change, but unless you can tell us what OS you are running, including version, we don't have a foundation to build upon. -- richard > > My application does a fair bit of caching and prefetching, so I have > zfetch disabled and primarycache set to only metadata. Also, reads > happen (on a per client basis) relatively infrequently, so I can easily > take it if the pool stops reading for a few seconds and just writes > data. The problem is, ZFS starts alternating between reads and writes > really quickly, which in turn starves me on IOPS and results in a huge > load spike. Judging on load numbers up to around 80 concurrent clients, > I suspect I could go up to 150 concurrent clients on this pool, but > because of this spike I top out at around 95-100 concurrent clients. > > Regards, > -- > Saso > _______________________________________________ > 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
