[arch-general] Samsung NVMe set up

[Alan E. Davis]

Thank you for the helpful information and advice.

I apologize for linking to ads.

How I connect NVMe would affect performance.  I see that my assumptions
about the numbers are pretty naive.

Looking at the specs for a pretty fast conventional hard drive,  a Hitachi
Ultrastar  HUA723020ALA641 , many different numbers jump off the page:

Interface transfer rate: 600MB/s
Interface: 6.0 Gb/s
Media Transfer Rate: 207 MB/s (max)
My Results:
$ sudo hdparm -Tt --direct /dev/sda

/dev/sda:
 Timing O_DIRECT cached reads:   680 MB in  2.00 seconds = 339.83 MB/sec
 Timing O_DIRECT disk reads: 430 MB in  3.01 seconds = 142.78 MB/sec

For the NVMe drive, I see that it is *up to* 3.2 GB/s, or 3200MB/s, and
this may be "up-to" that speed..

I see also that this depends on many factors.  So perhaps I ought to be
happy with these results:
  Timing O_DIRECT cached reads:   2506 MB in  2.00 seconds = 1252.75 MB/sec
 Timing O_DIRECT disk reads: 5088 MB in  3.00 seconds = 1695.50 MB/sec

 I did not see, right of the bat, numbers that are comparable  to Media
transfer Rate.

Comparing these numbers: 10X the "direct disk read" speeds is ok with me.

I still don't understand what options would be best in /etc/fstab for the
NVMe M.2 drive.  I have noticed various conjectures and ideas about
discards or trim.  I don't want to damage the new unit through ignorance.

Thanks.

Alan

On Mon, Jun 19, 2017 at 8:12 PM, Dragon ryu <knight.ryu12 at gmail.com> wrote:

>
>
> 2017/06/20 午前9:16 "Sean Greenslade" <sean at seangreenslade.com>:
>
> A couple of notes:
>
> On Sun, Jun 18, 2017 at 10:21:33PM -0700, Alan E. Davis via arch-general
> wrote:
> > Hello everyone:
> >
> > I built a new machine with a Samsung SSD 960 EVO NVMe
> > <https://www.googleadservices.com/pagead/aclk?sa=L&ai=DChcSE
> wjWxp_rk8nUAhWBfn4KHadiANoYABABGgJwYw&ohost=www.google.com&
> cid=CAESEeD2DLyQ7hEOLOBgSPqc9iEd&sig=AOD64_35gPrHU2xXVzC269P
> D9qfp0UjlwQ&ctype=5&q=&ved=0ahUKEwi6nZrrk8nUAhUE42MKHXAuDBsQww8ILA&adurl=
> >Samsung
> > SSD 960 EVO NVMe
> > <https://www.googleadservices.com/pagead/aclk?sa=L&ai=DChcSE
> wjWxp_rk8nUAhWBfn4KHadiANoYABABGgJwYw&ohost=www.google.com&
> cid=CAESEeD2DLyQ7hEOLOBgSPqc9iEd&sig=AOD64_35gPrHU2xXVzC269P
> D9qfp0UjlwQ&ctype=5&q=&ved=0ahUKEwi6nZrrk8nUAhUE42MKHXAuDBsQww8ILA&adurl=
> >Samsung
> > 950 EVO NVMe M.2 500GB component.
>
> Please don't link to ads. A page like this is much more appropriate:
>
> http://www.samsung.com/semiconductor/minisite/ssd/product/
> consumer/960evo.html
>
> > Installation went swell.  I was able to
> > use bootctl (by whatever name), which seemed to be easier than using
> GRUB.
> > (on the Manjaro wiki was found an extremely coherent discussion of this
> > system).  I have encountered no problems other than slow-ish (if one
> would
> > call it that).
> >
> > When I run hdparm to test the performance of this memory, it falls far
> > short of the specification of 32 Gb/s.
>
> Where did you get that number? All the specs I see for these drives show
> transfer rates in MB/s. You may have confused the read/write specs of
> the drive with the link speed of the NVMe / PCIe bus. The two are not
> the same.
>
> Also note that the read/write speeds are spec'd as "up to" speeds, so
> they are not guaranteeing any minimum speeds. Perhaps I'm just jaded,
> but I would be happy to get anything close to a spec-sheet speed on
> consumer hardware.
>
> > I realize that the Linux kernel has
> > recently included some code for the NVME drivers.  There is also some
> > question as to the best parameters to use in /etc/fstab.
>
> That will depend entirely on the filesystem you choose. Also note that
> real-world filesystems rarely do perfectly sequential reads or writes,
> so your real world read/write performance will almost certainly be lower
> than any HDD test utility shows.
>
> --Sean
>
> Also, it is depends on "How you connect NVMe" and "How M/B handles it",
> also "what filesystem you use".
>
>


-- 
[I do not] carry such information in my mind since it is readily
available in books. …The value of a college education is not the
learning of many facts but the training of the mind to think.
          ---Albert Einstein



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