On Wed, Sep 17, 2008 at 10:55 AM, Bob Friesenhahn < [EMAIL PROTECTED]> wrote:
> Each write to a vdev causes a write to all the disks in that vdev. This > means that the write consumes at least one IO from each of the involved > disks. That write does not cause any activity in the non-involved vdevs. So I infer from the previous and next paragraph that a read operation on a raidz2 vdev incurs a read operation on each disk member of the vdev. > As a general rule, multi-user performance should improve linearly with the > number of vdevs since each vdev contributes a disk's share of IOPS. > However, in the special case where the vdevs are mirrors, the read > performance can be doubled since the read may be done independently from > each side of the mirror, thereby doubling the available read IOPS. I will also infer that this differs from traditional RAID5/6 setups in that parity is only read when the array is degraded due to disk failure or rebuilding an array. A zpool therefore has read operation overhead associated with what is refered to as checksumming.
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