Re: dd performance [was Re: Call for Foundation-supported Project Ideas]

I intentionally used dd without the bs parameter, as I do care less
about "maximum speed" than clearing the drives completely and also do
a lot of I/O transactions.
The latter because drives that are becoming unreliable tend to
occasionally throw errors, and the more I/O transactions one does the
better the chance is to spot this kind of drives.

The system is a HP Z420, the mainboard/chipset/controller specs can be
found in the web.
The drives in question here (quite old) 2TB WD Black enterprise grade
3.5" SATA drives. Their SMART data is good, not hinting at any
problems.

On Linux, erasing them both concurrently finished at almost the same time.
Thus I do not really understand why on FreeBSD this is so much different.

On 12/2/21, Alan Somers <asomers@freebsd.org> wrote:
> This is very surprising to me.  I never see dd take significant CPU
> consumption until the speed gets up into the GB/s range.  What are you
> using for the bs= option?  If you set that too low, or use the
> default, it will needlessly consume extra CPU and IOPs.  I usually set
> it to 1m for this kind of usage.  And what kind of HDDs are these,
> connected to what kind of controller?
>
> On Thu, Dec 2, 2021 at 9:54 AM Stefan Blachmann <sblachmann@gmail.com>
> wrote:
>>
>> Regarding the suggestions to either improve or replace the ULE
>> scheduler, I would like to share another observation.
>>
>> Usually when I need to zero out HDDs using dd, I use a live Linux.
>> This time I did that on FreeBSD (13).
>> My observations:
>> - On the same hardware, the data transfer rate is a small fraction
>> (about 1/4th) of which is achieved by Linux.
>> - The first dd process, which erases the first HDD, gets almost all
>> CPU and I/O time. The second process which does the second HDD is
>> getting starved. It actually really starts only after the first one
>> finished.
>>
>> To me it was *very* surprising to find out that, while erasing two
>> similar HDDs concurrently takes about one day on Linux, on FreeBSD,
>> the first HDD was finished after three days, and only after that the
>> remaining second dd process got the same CPU time, making it proceed
>> fast instead of creepingly slowly.
>>
>> So I guess this might be a scheduler issue.
>> I certainly will do some tests using the old scheduler when I got time.
>> And, I ask myself:
>> Could it be a good idea to sponsor porting the Dragonfly scheduler to
>> FreeBSD?
>>
>> On 12/2/21, Johannes Totz <jo@bruelltuete.com> wrote:
>> > On 29/11/2021 03:17, Ed Maste wrote:
>> >> On Sun, 28 Nov 2021 at 19:37, Steve Kargl
>> >> <sgk@troutmask.apl.washington.edu> wrote:
>> >>>
>> >>> It's certainly not the latest and greatest,
>> >>> CPU: Intel(R) Core(TM)2 Duo CPU     T7250  @ 2.00GHz (1995.04-MHz
>> >>> K8-class CPU)
>> >>
>> >> If you're content to use a compiler from a package you can save a lot
>> >> of time by building with `CROSS_TOOLCHAIN=llvm13` and
>> >> `WITHOUT_TOOLCHAIN=yes`. Or, instead of WITHOUT_TOOLCHAIN perhaps
>> >> `WITHOUT_CLANG=yes`, `WITHOUT_LLD=yes` and `WITHOUT_LLDB=yes`.
>> >
>> > (re-send to list, sorry)
>> > Can we disconnect the compiler optimisation flag for base and clang? I
>> > don't need the compiler to be build with -O2 but I want the resulting
>> > base system to have optimisations enabled.
>> > Right now, looks like both get -O2 and a lot of time is spent on
>> > optimising the compiler (for no good reason).
>> >
>> >
>>
>