Re: discard synchronous on most SSDs?

Marc MERLIN
2014-03-16T06:06:44Z

On Sat, Mar 15, 2014 at 11:26:27AM +0000, Duncan wrote:
> Chris Samuel posted on Sat, 15 Mar 2014 17:48:56 +1100 as excerpted:
>
> > $ sudo smartctl --identify /dev/sdb | fgrep 'Trim bit in DATA SET
> > MANAGEMENT'
> > 169 0 1 Trim bit in DATA SET MANAGEMENT command
> > supported
> > $
> >
> > If that command returns nothing then it's not reported as supported (and
> > I've tested that). You can get the same info with hdparm -I.
>
> > My puzzle now is that I have two SSD drives that report supporting NCQ
> > TRIM (one confirmed via product info) but report only supporting SATA
> > 3.0 not 3.1.
>
> My SATA 2.5 SSDs reported earlier, report support for it too, so it's
> apparently not SATA 3.1 limited. (Note that I'm simply grepping word
> 169, in the command below. Since word 169 is trim support...)
>
> sudo smartctl --identify /dev/sda | grep '^ 169'
> 169 - 0x0001 Data Set Management support
> 169 0 1 Trim bit in DATA SET MANAGEMENT command supported
>
> Either that or that feature bit simply indicates trim support, not NCQ
> trim support.

Mmmh, so now I'm confused.

See this:

=== START OF INFORMATION SECTION ===
Device Model: INTEL SSDSC2BW180A3L
Serial Number: CVCV215200XU180EGN
LU WWN Device Id: 5 001517 bb28c5317
Firmware Version: LE1i
User Capacity: 180,045,766,656 bytes [180 GB]
Sector Size: 512 bytes logical/physical
Rotation Rate: Solid State Device
Device is: Not in smartctl database [for details use: -P showall]
ATA Version is: ACS-2 (minor revision not indicated)
SATA Version is: SATA 3.0, 3.0 Gb/s (current: 3.0 Gb/s)
Local Time is: Sat Mar 15 15:49:06 2014 PDT
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

polgara:/usr/src# smartctl --identify /dev/sda | grep '^ 169'
169 - 0x0001 Data Set Management support
169 0 1 Trim bit in DATA SET MANAGEMENT command supported

This is a super old SSD from 3 years ago. Clearly it can't support
synchronous dicard, right?

Yet, deleting a kernel tree also takes 1.5 seconds:
polgara:/usr/src# time rm -rf linux-3.14-rc5/
real 0m1.441s
user 0m0.048s
sys 0m1.352s

So maybe it's not the data level, but just the value of 169?

Either way, this SSD is more than 2 years old, maybe 3 actually.

Marc
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