-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I've started porting a video streaming application to opensolaris on ZFS, and am hitting some pretty weird performance issues. The thing I'm trying to do is run 77 concurrent video capture processes (roughly 430Mbit/s in total) all writing into separate files on a 12TB J4200 storage array. The disks in the array are arranged into a single RAID-0 ZFS volume (though I've tried different RAID levels, none helped). CPU performance is not an issue (barely hitting 35% utilization on a single CPU quad-core X2250). I/O bottlenecks can also be ruled out, since the storage array's sequential write performance is around 600MB/s.
The problem is the bursty behavior of ZFS writes. All the capture processes do, in essence is poll() on a socket and then read() and write() any available data from it to a file. The poll() call is done with a timeout of 250ms, expecting that if no data arrives within 0.25 seconds, the input is dead and recording stops (I tried increasing this value, but the problem still arises, although not as frequently). When ZFS decides that it wants to commit a transaction group to disk (every 30 seconds), the system stalls for a short amount of time and depending on the number capture of processes currently running, the poll() call (which usually blocks for 1-2ms), takes on the order of hundreds of ms, sometimes even longer. I figured that I might be able to resolve this by lowering the txg timeout to something like 1-2 seconds (I need ZFS to write as soon as data arrives, since it will likely never be overwritten), but I couldn't find any tunable parameter for it anywhere on the net. On FreeBSD, I think this can be done via the vfs.zfs.txg_timeout sysctl. A glimpse into the source at http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/fs/zfs/txg.c on line 40 made me worry that somebody maybe hard-coded this value into the kernel, in which case I'd be pretty much screwed in opensolaris. Any help would be greatly appreciated. Regards, - -- Saso -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAks0/QoACgkQRO8UcfzpOHB9PgCeOuJFVHTCohRzuf7kAEkC1l1i qBAAn18Jkx+N9OotWVCwpz5iQzNZSsEG =FCJL -----END PGP SIGNATURE----- _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
