Monitoring IO Accelerator health
NAND flash and component failure
The IO Accelerator is a highly fault-tolerant storage subsystem that provides many levels of protection against component failure and the loss nature of solid state storage. However, as in all storage subsystems, component failures might occur.
When a large enough number of data blocks is retired due to error, the NAND flash media is considered worn out. By properly selecting NAND flash media for the hosted application and proactively monitoring device age and health, you can assure reliable performance over the intended product life.
Health metrics
The IO Accelerator driver manages block retirement using pre-determined retirement thresholds. The IO Accelerator Management Tool and the fio-statusutility show a health indicator that starts at 100 and counts down to 0. As certain thresholds are crossed, various actions are taken.
At the 10% healthy threshold, a one-time warning is issued. For methods for capturing this alarm event, see "Health monitoring techniques (on page 54)."
At 0%, the device is considered unhealthy. It enters write-reduced mode, which somewhat prolongs its lifespan so data can be safely migrated. In this state, the IO Accelerator behaves normally except for the reduced write performance.
At some point after the 0% threshold, the device enters read-only mode. Any attempt to write to the IO Accelerator causes an error. Some file systems might require special mount options to mount a read-only block device, beyond specifying that the mount should be read-only. For example, under Linux, ext3 requires that -o ro,noload is used. The noload option tells the file system not to try to replay the journal.
Read-only mode should be considered a final opportunity to migrate data off the device since device failure is more likely with continued use.
The IO Accelerator might enter failure mode. In this case, the device is offline and inaccessible. This can be caused by an internal catastrophic failure, improper firmware upgrade procedures, or device wears out.
Health monitoring techniques
fio-status
Output from the fio-statusutility shows the health percentage and drive state. These items are in bold in the following sample output.
Found 1 ioDrive in this system
Fusion-io driver version: 2.1.0 build 19032
Adapter: ioDrive
HP 160GB SLC PCIe ioDrive for ProLiant Servers, Product Number:600278-B21
Monitoring IO Accelerator health 54
