One of the new features of vSphere 5.1 was the SSD monitoring and I/O Device Management features which I discussed in this post. I was doing some further testing on this recently and noticed that a number of fields from my SSD were reported as N/A. For example, I ran the following command against a local SSD drive on my host and these were the statistics returned.
So why were so many statistics coming back as N/A from my SSD drive? The reason is that the SMART utility (smartd – new to vSphere 5.1) gets information from the ATA device by sending an ATA SMART command. As per the SMART specification there are about 100+ unique attributes which a device can export for diagnostic purposes. Unfortunately not all vendors implement all the values as there are limited resources on the hard disk controller. Therefore vendors just implement whatever attributes they like to monitor and provide them as part of the SMART data command.
The smartd collects information from ATA devices, but if the device does not provide a value for a particular attribute, then we will show N/A. It is very well possible that this SSD device is not be providing those values.
It should be noted that bespoke plugins from the various drive vendors can also be added to vSphere 5.1 to display specific capabilities and attributes for their own drives.
Get notification of these blogs postings and more VMware Storage information by following me on Twitter: @VMwareStorage