Disk: I/O Bytes

This statistic shows the back-end throughput to the disks, in I/O bytes per second, after Oracle ZFS Storage Appliance has processed logical I/O into physical I/O based on share settings and software RAID settings. To configure the RAID settings, see Configuring Storage in Oracle ZFS Storage Appliance Administration Guide, Release OS8.8.x.

For example, an 8 Kbyte write over NFSv3 can become a 128 Kbyte write after the record size is applied from the share settings, which can then become a 256 Kbyte write to the disks after mirroring is applied, plus additional bytes for filesystem metadata. On the same mirrored environment, an 8 Kbyte NFSv3 read can become a 128 Kbyte disk read after the record size is applied; however, this does not get doubled by mirroring (the data only needs to be read from one half of the mirrored environment). It can help to monitor throughput at all layers at the same time to examine this behavior; for example, by viewing:

• Network: Device Bytes - Data rate on the network (logical)

• Disk: ZFS Logical I/O Bytes - Data rate to the share (logical)

• Disk: I/O Bytes - Data rate to the disks (physical)

When viewing the I/O bytes per second broken down by operation type, the operation pane shows the read and write statistics. Select an operation in the pane to highlight it and display it separately, by color, in the graph. Select an already highlighted operation to not display it separately in the graph.

When viewing the I/O bytes per second broken down by disk, the disk breakdown pane shows the statistics per the name of the storage pool disk or system disk. Select a disk in the disk breakdown pane to highlight it and display it separately, by color, in the graph. Select an already highlighted disk to not display it separately in the graph. When mousing over a disk in this pane, a box displays the following information:

• Disk name - Controller or disk shelf name/label: I/O bytes per second

• Disk Type: - Typically HDD or SSD

• Type: - Typically System, Data, Cache, or Log

• Size

• RPM - Not displayed for SSDs

To display the hierarchy view for all disks, click View Hierarchy, below the disk breakdown pane. The I/O bytes per second are shown for the controller and each disk shelf. Click Refresh hierarchy to refresh the hierarchical breakdown visible in the graph. To close this view, click the close icon .

When to Check I/O Bytes

Use this statistic to understand the nature of back-end disk I/O, based on bytes, after an issue based on disk utilization or latency has been observed. It is difficult to identify an issue from disk I/O throughput alone: A single disk might be performing well at 50 Mbytes/sec (sequential I/O), yet poorly at 5 Mbytes/sec (random I/O).

Use the disk breakdown pane and the hierarchy view to determine if the disk shelves are balanced in regard to disk I/O throughput. When examining disk throughput, it is common that cache and log devices have higher throughput than other storage pool disks.

I/O Bytes Breakdowns

Table 5-31 Breakdowns of I/O Bytes

Breakdown	Description
type of operation	Read or write.
disk	Storage pool disk or system disk. This breakdown can identify system disk I/O versus pool disk I/O, and I/O to cache and log devices.

Further Analysis

For the best measure of disk utilization, see Disk: Disks. To examine operations/second instead of bytes/second, see Disk: I/O Operations.