ACS-2 Long and Short Term Endurance Indicators February 13, 2009 Revision 0 Technical Editor: Jim Hatfield 389 Disc Drive Longmont, CO 80503 720-684-2120 James.C.Hatfield@Seagate.com Long and Short Term Endurance Indicators 1
T13/e09101r0 February 13, 2009 Document Status Revision History Rev Date Description 0 February 13, 2009 1) Initial Revision 1) 2 Long and Short Term Endurance Indicators
1 Introduction This proposal introduces two new health indicators for solid state storage. These Device Statistics are intended to be placed in the same page as the existing Percentage Used Endurance Indicator. 2 Changes to ACS-2 0.0.1 Solid State Statistics (Page TBD) [ Editors note: put this in Annex A, in the Device Statistics log] 0.0.1.1 Overview Device Statistics log page TBD contains information about the device as described in table TBD. a) Percentage Used Endurance Indicator. b) Short-Term Endurance Indicator c) Long-Term Endurance Indicator 2.0.0.1 Endurance (Informative) Because the short-term and long-term indicators provide values in units of time, the values may significantly change either higher or lower based on the device interface activity. Continuous high interface traffic results, at least temporarily, in a significantly lower remaining device life prediction than an idle interface condition because the estimates are based on a sustained continuation of the conditions during the calculation interval. An analogy to fuel consumption helps to explain the variability in the values returned by these statistics and how they relate to each other. One item to remember is that in this analogy, the fuel tank cannot be refilled. Short term Speeding up a hill: If consumption is continued at this rate, the fuel tank empties at a faster rate than average. Coasting downhill: If consumption is continued at this rate, the fuel tank empties at a significantly slower rate than average. Parked in the garage: The fuel tank does not empty at all. Long term Since this statistic involves a longer period of time, much of the uneven terrain mentioned in the short term situation is averaged out. This estimate provides an indication of how fast the fuel tank empties over a relatively short term compared to the life of the product, but may vary significantly based on the number of miles driven during the past week. In either case, the Percent Used Endurance Indicator statistic provides a reading analogous to the fuel gauge and is the statistic that should be used in determining the condition of the device. The short term and long term indicators provide an indication of how the Percent Used Endurance Indicator will change over time based on the current activity level of the device. Long and Short Term Endurance Indicators 3
T13/e09101r0 February 13, 2009 0.0.1.2 Percentage Used Endurance Indicator 0.0.1.2.1 Description Description The Percentage Used Endurance Indicator is an vendor specific estimate of the percentage of device life used based on the actual device usage and the manufacturer's prediction of device life. A value of 100 indicates that the estimated endurance of the device has been consumed, but may not indicate a device failure (e.g., minimum power-off data retention capability reached for devices using NAND flash technology). The value is allowed to exceed 100. The volatile value shall be updated once per power-on hour independent of the update interval specified below. 0.0.1.2.2 Update Interval 0.0.1.2.3 Measurement Units Percent. 0.0.1.2.4 Initialization The Percentage Used Endurance Indicator shall be initialized to zero at the time of manufacture. 0.0.1.3 Short-Term Endurance Indicator 0.0.1.3.1 Description Table 0.1 Solid State Statistics Offset Type Content TBD QWord Percentage Used Endurance Indicator (see TBD) 63:56 Device Statistics Flags (see table A.8). 55:8 Reserved 7:0 Percentage Used Endurance Indicator (DWord) TBD QWord Short-term Endurance Indicator (see TBD) 63:56 Device Statistics Flags (see table A.8). 55:32 Reserved 31:0 Short-term Endurance Indicator (DWord) TBD QWord Long-term Endurance Indicator (see TBD 63:56 Device Statistics Flags (see table A.8) 55:32 Reserved 31:0 Long-term Endurance Indicator (DWord) The Short-Term Endurance statistic is a vendor specific estimate of remaining device life based on the actual device usage during the previous power-on hour interval. This number may vary based on recent activity, remaining device capacity, and many other factors. Large changes in the value of this number should be 4 Long and Short Term Endurance Indicators
considered normal. A value of zero indicates that the estimated endurance of the device has been consumed, but may not indicate a device failure (e.g., minimum power-off data retention capability reached for devices using NAND flash technology). The volatile value shall be updated once per power-on hour independently of the update interval specified below. Reading this log shall not require the value to be updated. 0.0.1.3.2 Update Interval 0.0.1.3.3 Measurement Units Power-on hours. 0.0.1.3.4 Initialization The Short-Term Endurance Indicator shall not be valid until the device has completed one power-on hour and saved the value in a non-volatile location. 0.0.1.4 Long-Term Endurance Indicator 0.0.1.4.1 Description The Long-Term Endurance statistic is a vendor specific estimate of remaining device life based on the actual device usage during the previous 168 power-on hours. This number may vary based on recent activity, remaining device capacity, and many other factors. Large changes in the value of this number should be considered normal. A value of zero indicates that the estimated endurance of the device has been consumed, but may not indicate a device failure (e.g., minimum power-off data retention capability reached for devices using NAND flash technology). The volatile value shall be updated once per power-on hour independently of the update interval specified below. Reading this log shall not require the value to be updated. 0.0.1.4.2 Update Interval 0.0.1.4.3 Measurement Units Power-on hours. 0.0.1.4.4 Initialization The Long-Term Endurance Indicator shall not be valid until the device has completed 168 power-on hours and saved the value in a non-volatile location. Long and Short Term Endurance Indicators 5