Post by igork on Oct 7, 2021 15:42:48 GMT
Hi,
I have a question regarding PredictedMediaLifeLeftPercent attribute in Drive object.
Schema defines it as:
"PredictedMediaLifeLeftPercent": {
"type": [
"number",
"null"
],
"readonly": true,
"description": "The percentage of reads and writes that are predicted to still be available for the media",
"longDescription": "This property shall contain an indicator of the percentage of life remaining in the Drive's media."
}
We tried to implement it for NvMe Drive on our system, but we are a bit confused what is the right way to do it.
According to Swordfish specification (https://www.snia.org/sites/default/files/swordfish/release/v1.2.1c/pdf/Swordfish_v1.2.1c_NVMeMappingGuide.pdf):
6.9.2.8 NVMeEnduranceGroupProperties.PredictedMediaLifeLeftPercent
Property: NVMeEnduranceGroupProperties.PredictedMediaLifeLeftPercent “Percentage Used” in the Endurance Group Log. See 5.14.1.9
Type: Decimal %
Description: The percentage of reads and writes that are predicted to be available for the media.
LongDescription: This property shall contain an indicator of the percentage of life remaining in the drive’s media.
Notes: Inverse of “Percentage Used” in the Endurance Group Log. See 5.14.1.9 . Subtract the percentage used from 100% to report this value.
I also found the document (https://nvmexpress.org/wp-content/uploads/June-2019-Powering-the-Data-Center-with-NVM-Express.pdf) where Percentage Used described:
Percentage Used: Contains a vendor specific estimate of the percentage of life used for the Media Unit
based on the actual usage and the manufacturer’s prediction of NVM life. A value of 100 indicates that the
estimated endurance of the NVM in the Media Unit has been consumed, but may not indicate an NVM failure.
The value is allowed to exceed 100. Percentages greater than 254 shall be represented as 255. This value
shall be updated once per power-on hour when the controller is not in a sleep state.
Refer to the JEDEC JESD218A standard for SSD device life and endurance measurement techniques.
Since “Percentage Used” can exceed 100, then PredictedMediaLifeLeftPercent may become negative.
And according to Redfish specification I do not see any restriction that this attribute should be only positive.
But on the over hand general logic telling that % should be positive value.
Could you please explain if my understanding is right and we can have a negative PredictedMediaLifeLeftPercent for some cases.
Thank you,
Igor
I have a question regarding PredictedMediaLifeLeftPercent attribute in Drive object.
Schema defines it as:
"PredictedMediaLifeLeftPercent": {
"type": [
"number",
"null"
],
"readonly": true,
"description": "The percentage of reads and writes that are predicted to still be available for the media",
"longDescription": "This property shall contain an indicator of the percentage of life remaining in the Drive's media."
}
We tried to implement it for NvMe Drive on our system, but we are a bit confused what is the right way to do it.
According to Swordfish specification (https://www.snia.org/sites/default/files/swordfish/release/v1.2.1c/pdf/Swordfish_v1.2.1c_NVMeMappingGuide.pdf):
6.9.2.8 NVMeEnduranceGroupProperties.PredictedMediaLifeLeftPercent
Property: NVMeEnduranceGroupProperties.PredictedMediaLifeLeftPercent “Percentage Used” in the Endurance Group Log. See 5.14.1.9
Type: Decimal %
Description: The percentage of reads and writes that are predicted to be available for the media.
LongDescription: This property shall contain an indicator of the percentage of life remaining in the drive’s media.
Notes: Inverse of “Percentage Used” in the Endurance Group Log. See 5.14.1.9 . Subtract the percentage used from 100% to report this value.
I also found the document (https://nvmexpress.org/wp-content/uploads/June-2019-Powering-the-Data-Center-with-NVM-Express.pdf) where Percentage Used described:
Percentage Used: Contains a vendor specific estimate of the percentage of life used for the Media Unit
based on the actual usage and the manufacturer’s prediction of NVM life. A value of 100 indicates that the
estimated endurance of the NVM in the Media Unit has been consumed, but may not indicate an NVM failure.
The value is allowed to exceed 100. Percentages greater than 254 shall be represented as 255. This value
shall be updated once per power-on hour when the controller is not in a sleep state.
Refer to the JEDEC JESD218A standard for SSD device life and endurance measurement techniques.
Since “Percentage Used” can exceed 100, then PredictedMediaLifeLeftPercent may become negative.
And according to Redfish specification I do not see any restriction that this attribute should be only positive.
But on the over hand general logic telling that % should be positive value.
Could you please explain if my understanding is right and we can have a negative PredictedMediaLifeLeftPercent for some cases.
Thank you,
Igor
