Ben Rockwood wrote: > I need some help with clarification. > > My understanding is that there are 2 instances in which ZFS will write > to disk: > 1) TXG Sync > 2) ZIL > > Post-snv_87 a TXG should sync out when the TXG is either over filled or > hits the timeout of 30 seconds. > > First question is... is there some place I can see what this max TXG > size is? If I recall its 1/8th of system memory... but there has to be > a counter somewhere right? > There is both a memory throttle limit (enforced in arc_memory_throttle) and a write throughput throttle limit (calculated in dsl_pool_sync(), enforced in dsl_pool_tempreserve_space()). The write limit is stored as the 'dp_write_limit' for each pool.
> I'm unclear on ZIL writes. I think that they happen independently of > the normal txg rotation, but I'm not sure. > > So the second question is: do they happen with a TXG sync (expitied) or > independent of the normal TXG sync flow? > > Finally, I'm unclear on exactly what constitutes a TXG Stall. I had > assumed that it indicated TXG's that exceeded the alloted time, but > after some dtracing I'm uncertain. > I'm not certain what you mean by: "TXG Stall". > Any help is appreciated. > > benr. >
