Discussion SMR and Trim

[fzabkar]

The following thread would suggest that SMR drives make use of the ATA Trim command to optimise performance.

https://forum.hddguru.com/viewtopic.php?f=1&t=39014

Normally when new data are written to the drive, the data in the adjacent "shingles" needs to be cached and rewritten. However, if such data is marked as TRIM-med, then this operation becomes unnecessary. CMR drives don't need TRIM, so it would be an unnecessary overhead. This would suggest that one possible way to distinguish between CMR and SMR HDDs would be to examine Identify Device words 69 and 169. These data are reported by tools such as CrystalDiskInfo.

 

[popatim]

Interesting!

 

[fzabkar]

TRIM Command Support for WD External Drives:
https://support-en.wd.com/app/answers/detail/a_id/25185

WD external SSD drives and WD external HDD drives that have SMR (Shingled Magnetic Recording) drive inside, offer TRIM command support which is enabled by default in Windows 7 and above, designed to maintain the performance of SSD or HDD at an optimal level over the lifetime of the drive.
...
TRIM command support on the USB (SCSI) side is called UNMAP and the controller performs an UNMAP to TRIM translation.

 

[fzabkar]

This drive is a Host Managed SMR model, but it does not support Trim. Therefore it would appear that Trim is not supported by all SMR models.

Hard disk drive specifications Ultrastar® DC HC620 (previously known as Ultrastar Hs14 14TB/15TB):
https://documents.westerndigital.co...oduct-manual-ultrastar-dc-hc620-sata-spec.pdf

DATA SET MANAGEMENT

Bit Meaning

63 Set to one
62:1 Reserved
0 TRIM SUPPORTED bit (Not Supported)

 

[Diceman_2037]

Correction to WD's statement, Whilst Trim is possible on internal drives, the lack of scsi unmap and no native uasp on windows 7 means Trim is not sent to external usb connected devices.

eSATA and internal SATA support trim via ahci only on 7.

 

[fzabkar]

Here is an HD Tune read benchmark graph which shows a large spike where the SMR drive (WD40EZAZ) is serving up zeros for those sectors that have been TRIM-ed. The transfer rate in this case is equal to the max SATA speed.

https://forum.hddguru.com/viewtopic.php?f=1&t=43323

https://forum.hddguru.com/download/file.php?id=23801&mode=view (graph)