Bob Friesenhahn wrote: > On Wed, 26 Mar 2008, Neelakanth Nadgir wrote: >> When you experience the pause at the application level, >> do you see an increase in writes to disk? This might the >> regular syncing of the transaction group to disk. > > If I use 'zpool iostat' with a one second interval what I see is two > or three samples with no write I/O at all followed by a huge write of > 100 to 312MB/second. Writes claimed to be a lower rate are split > across two sample intervale. > > It seems that writes are being cached and then issued all at once. > This behavior assumes that the file may be written multiple times so a > delayed write is more efficient. >
This does sound like the regular syncing. > If I run a script like > > while true > do > sync > done > > then the write data rate is much more consistent (at about > 66MB/second) and the program does not stall. Of course this is not > very efficient. > This causes the sync to happen much faster, but as you say, suboptimal. Haven't had the time to go through the bug report, but probably CR 6429205 each zpool needs to monitor its throughput and throttle heavy writers will help. > Are the 'zpool iostat' statistics accurate? > Yes. You could also look at regular iostat and correlate it. -neel _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
