Question WD Ultrastar DC HC520 / HGST He12 50% slower in the center

[frherbers]

The WD Ultrastar DC HC520 / HGST He12 should have a transfer rate of 243MiB/sec.
This is true for the first two TBs, but than it degrades to only 50% in the center of the drive.

Used the following script to run 5 cycles. For each cycle measured the transfer rate at each start of a TB.

    #!/bin/bash
    for run in 1 2 3 4 5
    do
        for i in 11 0 1 2 3 4 5 6 7 8 9 10 11
        do
            echo "RUN=$run SKIP=$i"
            b=`expr 1024 \* 10`k
            s=`expr $i \* 100`KB
            c=`expr 1024 \* 1`
            dd if=/dev/sdg bs=$b iflag=direct skip=$s count=$c status=none | pv -b -t -r >/dev/null
            /usr/sbin/smartctl -a /dev/sdg | grep ^194     # show temperature
            echo
        done
    done

Each cycle showed the same transfer rate (there was no variation) at a specific TB start, independent of temperature.

SKIP=0 10.0GiB 0:00:42 [ 242MiB/s]
SKIP=1 10.0GiB 0:00:42 [ 242MiB/s]
SKIP=2 10.0GiB 0:00:43 [ 235MiB/s]
SKIP=3 10.0GiB 0:00:45 [ 226MiB/s]
SKIP=4 10.0GiB 0:00:46 [ 220MiB/s]
SKIP=5 10.0GiB 0:00:48 [ 210MiB/s]
SKIP=6 10.0GiB 0:00:50 [ 202MiB/s]
SKIP=7 10.0GiB 0:00:53 [ 192MiB/s]
SKIP=8 10.0GiB 0:00:57 [ 178MiB/s]
SKIP=9 10.0GiB 0:01:01 [ 166MiB/s]
SKIP=10 10.0GiB 0:01:08 [ 149MiB/s]
SKIP=11 10.0GiB 0:01:18 [ 129MiB/s]

RUN=1 33Celsius
RUN=2 39Celsius
RUN=3 42Celsius
RUN=4 43Celsius
RUN=5 44Celsius

Did somebody else notice this 50% drop of transfer rate for these drives?
Did you receive a sustainable transfer rate through the drive?
Hope to have some users running my script and showing their results for similar drives.

 

[Mr.Spock]

yes, because the outer tracks have a greater circumference, it could dip 40-50MB/s, note: there's less data towards the center so your avg transfer is still higher

most drives quote a sustained and max transfer rate - and it's usually "up to" not always

 

[USAFRet]

All spinning drives do this.
Constant RPM means that the outer tracks are going by faster than the inner.

 

[frherbers]

it could dip 40-50MB/s

These values I see on 3 Seagate IronWolf drives, which have similar specs, show a dip of 55MiB/s, this is some 25-30% dip.

Here we are talking of a 120MiB/s dip, a 50% dip.

there's less data towards the center so your avg transfer is still higher

Less data; looking at the last 3TB (which is 25% of the drive) the avg is 150MiB/s, which is 100MiB/s less on avg.

Didn't think I had to accept such a big drop of 50%.

 

[fzabkar]

Are you able to obtain a HD Tune read benchmark graph?

See https://hdtune.com/testresults.html

 

[fzabkar]

These values I see on 3 Seagate IronWolf drives, which have similar specs, show a dip of 55MiB/s, this is some 25-30% dip.

Sometimes a HDD manufacturer will create a smaller capacity model by taking a larger capacity and short-stroking it, possibly due to reasons of yield.

 

[popatim]

IIrc, center disk speed drop on those is typically only about 75MB/s but with drives that large, it wouldn't surprise if it has remapped sectors in that area right from the factory.

 

[Wu-Zi-Mu]

Drive speed drops off towards the center significantly on all HDDs, 2x dropoff is maybe a little big but 1.5x is typical for much smaller drives.

I reckon it drops off worse than smaller drives of that line because they left less empty space in the center of the platter. They had to fit in 12TB after all

 

[fzabkar]

These two Ironwolf (10TB & 12TB) graphs show a max/min ratio of around 2.2:

 

[popatim]

Oh center of the platter, I was thinking center of the drive ~7TB LoL