> Manoj Nayak wrote: >> 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. >> > > Yes, this is how it works for a read without errors. For a write, you > should see 4 writes, each 128KBytes/3. Writes may also be > coalesced, so you may see larger physical writes. > >> 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 ? >> > > No. vq_max_pending applies to each vdev.
4 disk raidz group issues 128k/3=42.6k io to each individual data disk.If 35 concurrent 128k IO is enough to saturate a disk( vdev ) , then 35*3=105 concurrent 42k io will be required to saturates the same disk. Thanks Manoj Nayak Use iostat to see what > the device load is. For the commonly used Hitachi 500 GByte disks > in a thumper, the read media bandwidth is 31-64.8 MBytes/s. Writes > will be about 80% of reads, or 24.8-51.8 MBytes/s. In a thumper, > the disk bandwidth will be the limiting factor for the hardware. > -- richard > > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
