Re: [zfs-discuss] Significant pauses during zfs writes
Hi Bob, Looks like : 6415647 Sequential writing is jumping http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6415647 -r Roch BourbonnaisSun Microsystems, Icnc-Grenoble Senior Performance Analyst 180, Avenue De L'Europe, 38330, Montbonnot Saint Martin, France Performance Availability Engineering http://icncweb.france/~rbourbon http://blogs.sun.com/roller/page/roch [EMAIL PROTECTED] (+33).4.76.18.83.20 Bob Evans writes: HI, Just getting my feet wet with zfs. I set up a test system (Sunblade 1000, dual channel scsi card, disk array with 14x18GB 15K RPM SCSI disks) and was trying to write a large file (10 GB) to the array to see how it performed. I configured the raid using raidz. During the write, I saw the disk access lights come on, but I noticed a peculiar behavior. The system would write to the disk, but then pause for a few seconds, then contineu, then pause for a few seconds. I saw the same behavior when I made a smaller raidz using 4x36 GB scsi drives in a different enclosure. Since I'm new to zfs, and realize that I'm probably missing something, I was hoping somebody might help shed some light on my problem. Thanks! This message posted from opensolaris.org ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Significant pauses during zfs writes
Yes James is right this is normal behaviour. Unless the writes are synchronous (O_DSYNC) or explicitely flushed (fsync()) then they are batched up, written out and committed as a transaction every txg_time (5 seconds). Neil. James C. McPherson wrote: Bob Evans wrote: Just getting my feet wet with zfs. I set up a test system (Sunblade 1000, dual channel scsi card, disk array with 14x18GB 15K RPM SCSI disks) and was trying to write a large file (10 GB) to the array to see how it performed. I configured the raid using raidz. During the write, I saw the disk access lights come on, but I noticed a peculiar behavior. The system would write to the disk, but then pause for a few seconds, then contineu, then pause for a few seconds. I saw the same behavior when I made a smaller raidz using 4x36 GB scsi drives in a different enclosure. Since I'm new to zfs, and realize that I'm probably missing something, I was hoping somebody might help shed some light on my problem. Hi Bob, I'm pretty sure that's not a problem that you're seeing, just ZFS' normal behaviour. Writes are coalesced as much as possible, so the pauses that you observed are most likely going to be the system waiting for suitable IOs to be gathered up and sent out to your storage. If you want to examine this a bit more then might I suggest the DTrace Toolkit's iosnoop utility. best regards, James C. McPherson ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss -- Neil ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Significant pauses during zfs writes
Neil Perrin writes: Yes James is right this is normal behaviour. Unless the writes are synchronous (O_DSYNC) or explicitely flushed (fsync()) then they are batched up, written out and committed as a transaction every txg_time (5 seconds). Neil. James C. McPherson wrote: Bob Evans wrote: Just getting my feet wet with zfs. I set up a test system (Sunblade 1000, dual channel scsi card, disk array with 14x18GB 15K RPM SCSI disks) and was trying to write a large file (10 GB) to the array to see how it performed. I configured the raid using raidz. During the write, I saw the disk access lights come on, but I noticed a peculiar behavior. The system would write to the disk, but then pause for a few seconds, then contineu, then pause for a few seconds. I saw the same behavior when I made a smaller raidz using 4x36 GB scsi drives in a different enclosure. Since I'm new to zfs, and realize that I'm probably missing something, I was hoping somebody might help shed some light on my problem. Hi Bob, I'm pretty sure that's not a problem that you're seeing, just ZFS' normal behaviour. Writes are coalesced as much as possible, so the pauses that you observed are most likely going to be the system waiting for suitable IOs to be gathered up and sent out to your storage. If you want to examine this a bit more then might I suggest the DTrace Toolkit's iosnoop utility. best regards, James C. McPherson ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss -- Neil ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss I also would agree if the application is burning 100% of a CPU. But if the application is being throttled at times _and_the storage is itself not 100% exercised then I believe something is wrong and we have that anomalous jumpyness. So Bob, is the application burning a full CPU ? -r ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Significant pauses during zfs writes
Hey, Bob - It might be worth exploring where your data stream for the writes was coming from. Moreover, it might be worth exploring how fast it was filling up caches for writing. Were you delivering enough data to keep the disks busy 100% of the time? I have been tricked by this before... :) Nathan. On Tue, 2006-08-15 at 01:38, James C. McPherson wrote: Bob Evans wrote: Just getting my feet wet with zfs. I set up a test system (Sunblade 1000, dual channel scsi card, disk array with 14x18GB 15K RPM SCSI disks) and was trying to write a large file (10 GB) to the array to see how it performed. I configured the raid using raidz. During the write, I saw the disk access lights come on, but I noticed a peculiar behavior. The system would write to the disk, but then pause for a few seconds, then contineu, then pause for a few seconds. I saw the same behavior when I made a smaller raidz using 4x36 GB scsi drives in a different enclosure. Since I'm new to zfs, and realize that I'm probably missing something, I was hoping somebody might help shed some light on my problem. Hi Bob, I'm pretty sure that's not a problem that you're seeing, just ZFS' normal behaviour. Writes are coalesced as much as possible, so the pauses that you observed are most likely going to be the system waiting for suitable IOs to be gathered up and sent out to your storage. If you want to examine this a bit more then might I suggest the DTrace Toolkit's iosnoop utility. best regards, James C. McPherson ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss -- ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
