Health Status

You can read your eMMC health status by using the mmc command and reading the EXT_CSD (extended card specific data) section. The life time estimation can be read for SLC and MLC areas as well as pre EOL status.

~# mmc extcsd read /dev/mmcblk1 | grep LIFE
eMMC Life Time Estimation A [EXT_CSD_DEVICE_LIFE_TIME_EST_TYP_A]: 0x01
eMMC Life Time Estimation B [EXT_CSD_DEVICE_LIFE_TIME_EST_TYP_B]: 0x01

~# mmc extcsd read /dev/mmcblk1 | grep EOL
eMMC Pre EOL information [EXT_CSD_PRE_EOL_INFO]: 0x01

The life time values are provided in 10% steps:

  • 0x01 = 0-10% device life time used

  • 0x02 = 10-20% device life time used

whereas life time estimation type A is for SLC eraseblocks and type B is for MLC eraseblocks.

The EOL information is an overall status for reserved blocks, given as follows:

  • 0x00 = Not defined

  • 0x01 = Normal: consumed less than 80% of the reserved blocks

  • 0x02 = Warning: consumed 80% of the reserved blocks

  • 0x03 = Urgent: consumed 90% of the reserved blocks

Write Reliability

Similar to the eMMC health status, you can check and set the write reliablity using the mmc command. The information reside also the EXT_CSD (extended card specific data) section. There are two parameters which are needed for the write reliability:


    • the LSB 1 defines if WR_REL_SET is writable

      • LSB = 1: writable

      • LSB = 0: read-only


    • shows the setup of reliable writing for each partition, whereas partition 1 starts at the LSB 1

      • WR_REL_SET = ext_csd[EXT_CSD_WR_REL_SET] | (1<<partition);

Check Write Reliability Setup

Check the write reliability setup by reading EXT_CSD from your device and filtering the two parameters:

~# mmc extcsd read /dev/mmcblk0 | grep WR_REL_PARAM
Write reliability parameter register [WR_REL_PARAM]: 0x05

~# mmc extcsd read /dev/mmcblk0 | grep WR_REL_SET
Write reliability setting register [WR_REL_SET]: 0x1f

Value Explanation:

  • WR_REL_PARAM = 0x05

    • The LSB in WR_REL_PARAM is set, which means that WR_REL_SET is writable. I.e. read-only would have shown WR_REL_PARAM: 0x04

  • WR_REL_SET = 0x1f

    • The LSB in WR_REL_SET is set, which means that reliable write is enable for partition 1. I.e. disabled would have shown WR_REL_SET = 0x1e

Enable Write Reliability

Enabling reliable writing can be done with the mmc command write_reliability set as seen in the help:

~# mmc --help
mmc write_reliability set <-y|-n|-c> <partition> <device>
        Enable write reliability per partition for the <device>.
        Dry-run only unless -y or -c is passed.
        Use -c if more partitioning settings are still to come.
        NOTE!  This is a one-time programmable (unreversible) change.

whereas a dry run can be made by providing the parameter -n.


Setting write reliability can only be done once (unreversible)!

Storage Information

The information described in the upper sections are as well collected by a small application called storage-info. This application reports the values in a human readable format to the file /run/storage/storage0.config:

~# cat /run/storage/storage0.config
Chip Name:                DG4008
HW Revision:              0x0
Revision:                 0x8
FW Version:               39102417
Serial Number:            0x65b0470c
Reliable Writable:        1
Reliable Write Config:    0x1f
Pre-EOL Information:      1 = Normal
Lifetime used (SLC):      10%
Lifetime used (MLC):      10%
Disk space free:          492.7MB



LSB = Least Significant Bit, the bit number 0 (bit with index 0)