Roch - PAE wrote: > Manoj Nayak writes: > > Hi All. > > > > ZFS document says ZFS schedules it's I/O in such way that it manages to > > saturate a single disk bandwidth using enough concurrent 128K I/O. > > The no of concurrent I/O is decided by vq_max_pending.The default value > > for vq_max_pending is 35. > > > > We have created 4-disk raid-z group inside ZFS pool on Thumper.ZFS > > record size is set to 128k.When we read/write a 128K record ,it issue a > > 128K/3 I/O to each of the 3 data disks in the 4-disk raid-z group. > > > > We need to saturate all three data disk bandwidth in the Raidz group.Is > > it required to set vq_max_pending value to 35*3=135 ? > > > > Nope. > > Once a disk controller is working on 35 requests, we don't > expect to get any more out of it by queueing more requests > and we might even confuse the firmware and get less. > > Now for an array controller and a vdev fronting for large > number of disks, then 35 might be a low number not allowing > full throughput. Rather than tuning 35 up, we suggest > splitting devives into smaller LUNs since each luns is given > a 35-deep queue. > > It means 4-disk raid-z group inside ZFS pool is exported to ZFS as a single device ( vdev ) .ZFS assigns vq_max_pending value of 35 to this vdev. To get higher throughput , I need to do following things ?
1.Reduce no of disks in the raidz group from four to three disk.So that same pending queue of 35 is available for lesser no of disk. 0r 2.Create slice out of physical disk & create raidz group out of four slices of a physical disk.So that same pending queue of 35 is available four slices of one physical disk. Thanks Manoj Nayak > Tuning vq_max_pending down helps read and synchronous write > (ZIL) latency. Today the preferred way to help ZIL latency > is to use a Separate Intent Log. > > -r > > > > Thanks > > Manoj Nayak > > _______________________________________________ > > 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
