Why is TRIM not supported on encrypted "/data" partition?

Question

I have a rooted Lenovo A369i. I use LagFix (fstrim) to TRIM partitions. Previously it was working well with /data but after I encrypted my phone it doesn't. I decrypted my phone by formatting. But now in the app it shows /data partition having kernel or hardware issues. It's not hardware because before encryption it was working well.

Answer 1

Just if someone stumbles upon this, following conditions should be met for TRIM to work:

• Underlying hardware (eMMC) must support TRIM. For instance Redmi Note 4 comes with MCP: RX1BMB which contains eMMC 5.1 and hence supports TRIM.

• Kernel must have support for TRIM, was added in v3.1, but it is disabled by default and vold daemon must map userdata partition with allow_discards option, which it didn't in my case.

  If your /data partition is encrypted (FDE), Support for allow_discards was added in version 1.11.0 (1) of device-mapper crypt ⁽¹⁾ target, but may not work e.g. on devices with Qualcomm SoCs. See this issue for more details.

• Filesystem must also support TRIM ⁽¹⁾ (except if you want to TRIM a whole partition with blkdiscard). Android uses ext4 or f2fs on /data partition, both support TRIM.

If these conditions meet, you can perform TRIM manually (fstrim -v /data) or periodically (scheduled service) or continuously (with discard mount option). See this answer for details on how often you should perform fstrim.