eG Monitoring
 

Measures reported by OraExaFlsLogTest

Exadata Smart Flash Logging, is the feature that writes to both hard disk and flash with the acknowledgement given as soon as either completes the write, thus improving response time and throughput.

Exadata Smart Flash Log reduces the average latency for performance-sensitive redo log write I/O operations, thereby eliminating performance bottlenecks that may occur due to slow redo log writes. Originally, Exadata Smart Flash Log was used to perform simultaneous writes to disk and flash storage. However, a further optimization known as Smart Flash Log Write-Back, uses Exadata Smart Flash Cache in Write-Back mode instead of disk storage.

In the event that the Flash Cache writes the data faster, the data need to be held only for a short time until the storage server is certain that all writes have made it to the redo log. Since the Smart Flash Log is only a temporary store, only a small amount of Flash cache is required-512MB per cell. If the flash logging feature is unavailable or could not be enabled, then the I/O operations to the redo log may slow down considerably thereby leading to performance bottlenecks. To eliminate such bottlenecks, it is it is necessary to keep track on the status of the flash log. The OraExaFlsLogTest test helps administrators to keep a vigil on the flash log!

This test auto-discovers the flash logs on the target storage server and for each flash log reports the status. This test also reveals the cell disks that are allocated to each flash cache and those cell disks that are unavailable. In addition, this test also reveals the size of the flash cache that is available for use. Using this test, administrators can figure out those flash caches that are in a critical state, isolate them and fix issues proactively. Also, administrators can figure out the flash cache that is currently being most utilized.

Outputs of the test: One set of the results for each flash log on the target Oracle Exadata Storage Server that is being monitored

Descriptor: Flash log

The measures made by this test are as follows:

Measurement Description Measurement Unit Interpretation
fLStatus Indicates the current status of this flash log.  

The table below indicates the values that this measure can report and their corresponding numeric equivalents:

Measure value Numeric Value
Normal 100
Import required 90
Critical 50

Note:

By default, this measure reports the above-mentioned Measure Values while indicating the current status of the flash log. However, in the graph of this measure, the status of the flash log will be represented using the corresponding numeric equivalents only.
cellDisks Indicates the number of cell disks allocated to this flash log. Number

The detailed diagnosis of this measure lists the names of the cell disks that are allocated to the flash log.
fLSize Indicates the total size of this flash log. GB

 

usableFLSize Indicates the amount of space that is available for use in this flash log. GB

 

fLefficiency Indicates the percentage of space that is available for use in this flash log. Percent

A value close to 0 indicates that the flash cache is running out of space.

unAvailableCellDisks Indicates the number of cell disks that are currently unavailable for this flash log. Number