Re: discard synchronous on most SSDs?

Marc MERLIN
2014-03-14T19:26:08Z

On Fri, Mar 14, 2014 at 12:07:54PM +0000, Duncan wrote:
> Marc MERLIN posted on Thu, 13 Mar 2014 22:17:50 -0700 as excerpted:
>
> > On Thu, Mar 13, 2014 at 09:39:02PM -0600, Chris Murphy wrote:
> >>
> >> On Mar 13, 2014, at 8:11 PM, Marc MERLIN <marc@merlins.org> wrote:
> >>
> >> > On Sun, Mar 09, 2014 at 11:33:50AM +0000, Hugo Mills wrote:
> >> >> discard is, except on the very latest hardware, a synchronous
> >> >> command (it's a limitation of the SATA standard), and therefore
> >> >> results in very very poor performance.
> >> >
> >> > Interesting. How do I know if a given SSD will hang on discard?
> >> > Is a Samsung EVO 840 1TB SSD latest hardware enough, or not? :)
> >>
> >> smartctl -a or -x will tell you what SATA revision is in place. The
> >> queued trim support is in SATA Rev 3.1. I'm not certain if this
> >> requires only the drive to support that revision level, or both
> >> controller and drive.
> >
> > I'm not sure I'm seeing this, which field is that?
>
> > ATA Version is: 8
> > ATA Standard is: ATA-8-ACS revision 4c
>
> Your drive didn't report it, but here, I have SATA fields as well, in
> addition to the ATA fields:
>
> Here's the fields from my Corsair Neutron SSDs:
>
> ATA Version is: ATA8-ACS (minor revision not indicated)
> SATA Version is: SATA 2.5, 6.0 Gb/s
>
> Here's the fields from my Seagate 500-gig 2.5-inch spinning rust:
>
> ATA Version is: ATA8-ACS T13/1699-D revision 4
> SATA Version is: SATA 2.6, 3.0 Gb/s

Ok, my smartmontools was too old. I got a newer one and now have proper
output:
Device Model: Samsung SSD 840 EVO 1TB
Serial Number: S1D9NEAD934600N
LU WWN Device Id: 5 002538 85009a8ff
Firmware Version: EXT0BB0Q
User Capacity: 1,000,204,886,016 bytes [1.00 TB]
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, ATA8-ACS T13/1699-D revision 4c
SATA Version is: SATA 3.1, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is: Fri Mar 14 10:49:39 2014 PDT
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

So I have Sata 3.1, that's great news, it means I can keep using discard
without worrying about performance and hangs

Thanks,
Marc
--
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Home page: http://marc.merlins.org/