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. 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
