Ran some performance tests as suggested. Machine A connects to machine B on a gigabit lan. Machine A sends 1024 1MB chucks of data; 1 GB in total. Machine B, the server, reads in the MB and writes it to a file. NOTE: server and client are little test programs written in C. Machine B (Server) hardware: - Single (no raid) Seagate Cheetah 70G Ultra320 15K - Quad Opteron 870 - 16G DDR400 - Backplane: LSI Logic / Symbios Logic 53c1030 PCI-X Fusion-MPT Dual Ultra320 SCSI (rev 8) Sync methods include: 1. mount with sync option - tried sync,dirsync which added no additional overhead 2. use O_SYNC open() flag 3. use fdatasync() just before closing the file - fsync() and fdatasync() produced the same results EXT2 tests ========================================== No sync 12.3 seconds (83 MB/Sec) mount=sync 44.3 seconds (23 MB/Sec) O_SYNC 31.7 seconds (32 MB/Sec) fdatasync() 31.3 seconds (32 MB/Sec) EXT3 tests =========================================== No sync data=writeback 14.5 seconds (70 MB/Sec) No sync data=ordered 17 seconds (60 MB/Sec) No sync data=journal 65 seconds (15 MB/Sec) data=ordered O_SYNC 49 seconds (20 MB/Sec) data=ordered,sync 52 seconds (19 MB/Sec) data=ordered fdatasync() 45.5 seconds (22 MB/Sec) data=journal O_SYNC 72.5 seconds (14 MB/Sec) data=journal,sync 81 seconds (12 MB/Sec) data=journal fdatasync() 60.5 seconds (17 MB/Sec) thanks Andreas Dilger <adilger@clusterfs.com> wrote:<blockquote class="replbq" style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"> On Mar 21, 2007 16:51 -0700, brian stone wrote: > My application always needs to sync file data after writing. I don't want anything handing around in the kernel buffers. I am wondering what is the best method to accomplish this. > 4. Do I use EXT3 in full journaled mode, where the data and metadata are journaled? In this case, is the journaled data sync'd or async'd? When the journal commits the data to the file system, is that sync'd or dumped into kernel buffers? > > 5. Since I will always be syncing the data, does it make any sense to use EXT3? It feels like the EXT3 journal would be unnecessary. In theory, ext3 + data=journal will give you the best performance, because sync IO will always be linear IO to the journal. Unless your filesystem is constantly busy, then the writes to the filesystem can happen asynchronously after being committed to the journal without danger of being lost. That said, nothing better than benchmarking your app with different filesystem options to see which one is best. Cheers, Andreas -- Andreas Dilger Principal Software Engineer Cluster File Systems, Inc. </blockquote> <hr size=1>No need to miss a message. <a href="http://us.rd.yahoo.com/evt=43910/*http://mobile.yahoo.com/mail ">Get email on-the-go </a> with Yahoo! Mail for Mobile. <a href="http://us.rd.yahoo.com/evt=43910/*http://mobile.yahoo.com/mail ">Get started.</a>