OK, I tried it with txg_time set to 1 and am seeing less predictable results. The first time I ran the test it completed in 27 seconds (vs 24s for ufs or 42s with txg_time=5). Further tests ran from 27s to 43s, about half the time greater than 40s.
zpool iostat doesn't show the large no-writes gaps, but it is still very bursty and peak bandwidth is lower. Here is a 29s run: tank 113K 464G 0 0 0 0 tank 113K 464G 0 226 0 28.2M tank 40.1M 464G 0 441 0 46.9M tank 88.2M 464G 0 384 0 39.8M tank 136M 464G 0 445 0 47.4M tank 184M 464G 0 412 0 43.4M tank 232M 464G 0 411 0 43.2M tank 272M 464G 0 402 0 42.1M tank 320M 464G 0 435 0 46.3M tank 368M 464G 0 366 63.4K 37.7M tank 408M 464G 0 494 0 53.6M tank 456M 464G 0 360 0 36.8M tank 496M 464G 0 420 0 44.5M tank 544M 463G 0 439 0 46.8M tank 585M 463G 0 370 0 38.2M tank 633M 463G 0 407 0 42.6M tank 673M 463G 0 457 0 49.0M tank 713M 463G 0 368 0 37.9M tank 761M 463G 0 443 0 47.2M tank 801M 463G 0 380 63.4K 39.4M tank 844M 463G 0 444 63.4K 47.4M tank 879M 463G 0 184 0 14.9M tank 879M 463G 0 339 0 33.4M tank 913M 463G 0 215 0 26.5M tank 944M 463G 0 393 63.4K 36.4M tank 976M 463G 0 171 63.4K 10.5M tank 1008M 463G 0 237 63.4K 21.6M tank 1008M 463G 0 312 0 31.5M tank 1.02G 463G 0 137 0 9.05M tank 1.05G 463G 0 313 0 23.4M tank 1.05G 463G 0 0 0 0 Jesse > Jesse, > > This isn't a stall -- it's just the natural rhythm of > pushing out > transaction groups. ZFS collects work (transactions) > until either > the transaction group is full (measured in terms of > how much memory > the system has), or five seconds elapse -- whichever > comes first. > > Your data would seem to suggest that the read side > isn't delivering > data as fast as ZFS can write it. However, it's > possible that > there's some sort of 'breathing' effect that's > hurting performance. > One simple experiment you could try: patch txg_time > to 1. That > will cause ZFS to push transaction groups every > second instead of > the default of every 5 seconds. If this helps (or if > it doesn't), > please let us know. > > Thanks, > > Jeff > > Jesse DeFer wrote: > > Hello, > > > > I am having problems with ZFS stalling when > writing, any help in troubleshooting would be > appreciated. Every 5 seconds or so the write > bandwidth drops to zero, then picks up a few seconds > later (see the zpool iostat at the bottom of this > message). I am running SXDE, snv_55b. > > > > My test consists of copying a 1gb file (with cp) > between two drives, one 80GB PATA, one 500GB SATA. > The first drive is the system drive (UFS), the > second is for data. I have configured the data > drive with UFS and it does not exhibit the stalling > problem and it runs in almost half the time. I have > tried many different ZFS settings as well: > atime=off, compression=off, checksums=off, > zil_disable=1 all to no effect. CPU jumps to about > 25% system time during the stalls, and hovers around > 5% when data is being transferred. > > # zpool iostat 1 > capacity operations bandwidth > sed avail read write read write > > ---------- ----- ----- ----- ----- ----- > ----- > tank 183M 464G 0 17 1.12K 1.93M > tank 183M 464G 0 457 0 57.2M > tank 183M 464G 0 445 0 55.7M > tank 183M 464G 0 405 0 50.7M > tank 366M 464G 0 226 0 4.97M > tank 366M 464G 0 0 0 0 > tank 366M 464G 0 0 0 0 > tank 366M 464G 0 0 0 0 > tank 366M 464G 0 200 0 25.0M > tank 366M 464G 0 431 0 54.0M > tank 366M 464G 0 445 0 55.7M > tank 366M 464G 0 423 0 53.0M > tank 574M 463G 0 270 0 18.1M > tank 574M 463G 0 0 0 0 > tank 574M 463G 0 0 0 0 > tank 574M 463G 0 0 0 0 > tank 574M 463G 0 164 0 20.5M > tank 574M 463G 0 504 0 63.1M > tank 574M 463G 0 405 0 50.7M > tank 753M 463G 0 404 0 42.6M > tank 753M 463G 0 0 0 0 > tank 753M 463G 0 0 0 0 > tank 753M 463G 0 0 0 0 > tank 753M 463G 0 343 0 42.9M > tank 753M 463G 0 476 0 59.5M > tank 753M 463G 0 465 0 50.4M > tank 907M 463G 0 68 0 390K > tank 907M 463G 0 0 0 0 > tank 907M 463G 0 11 0 1.40M > tank 907M 463G 0 451 0 56.4M > tank 907M 463G 0 492 0 61.5M > tank 1.01G 463G 0 139 0 7.94M > tank 1.01G 463G 0 0 0 0 > > Thanks, > Jesse DeFer This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
