I optimized my 1TB Crucial SATA SSD and observed an increase of 64.2MB in the Host Writes count.

838GiB -- total size of C: volume
142GiB -- free space in C: volume

Host writes before optimize -- 0x17b8ed77f
Host writes after optimize -- 0x17b90c19f

0x17b90c19f - 0x17b8ed77f = 125472
(0x17b90c19f - 0x17b8ed77f) x 512 bytes = 64.2 MB

I confirmed that the units for the Host Writes attribute were single sectors by writing a 1.3GB file and comparing the before-and-after counts.

The OS was Windows 10.

_________________
A backup a day keeps DR away.

And one TRIM command generates at least 1 sector worth of host writes. AFAIK per command max 2 GB can be trimmed. To TRIM his 64 GB drive 32 sectors worth of host writes would be required, if I understand and remember correctly.

_________________
Joep - http://www.disktuna.com - video & photo repair & recovery service

The ATA standard defines DATA SET MANAGEMENT (06h) and DATA SET MANAGEMENT XL (07h) commands.

For the former ...

63:48 RANGE LENGTH field
47:0 LBA VALUE field

For the latter ...

127:64 RANGE LENGTH field
63:48 Reserved
47:0 LBA VALUE field

My take on the SMART Host Writes attribute is that it counts ATA WRITE SECTOR(S) commands (30h). If that's the case, then TRIM commands should not affect this counter. If this were not the case, then READ SECTOR(S) commands (20h) would also increment the Host Writes counter.

_________________
A backup a day keeps DR away.

Read sector does not send 512 bytes of data to the drive, TRIM does. It provides a "map" of LBA ranges to be trimmed, a range list as a data block. I think this is what's going on and why it is counted as host write.

_________________
Joep - http://www.disktuna.com - video & photo repair & recovery service

Oops, brain fart. I was thinking of SMART READ LOG commands and confused myself. I wonder if IDENTIFY DEVICE increments the host reads counter for the same reason?

_________________
A backup a day keeps DR away.