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

frherbers

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Jan 19, 2020
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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.

Code:
#!/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.
 

Blue Fox

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This is normal for any hard drive and is just simple geometry. You will only get peak speeds on the outer tracks.
 

drescherjm

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The only time this is not the case for a spinner is when the inner tracks are not used. Some enterprise drives used to short stroke the drive ( not use the entire platter).
 

frherbers

n00b
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Jan 19, 2020
Messages
2
On 3 Seagate IronWolf drives, which have similar specs, show a dip of 55MiB/s, this is some 25% dip.

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

Blue Fox

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Once again, normal. 3.5" drive platters are approximately 5cm in radius, with the inner tracks being approximately 2cm in radius on account of the spindle. Quick math says the outer tracks have approximately 31cm linear distance per revolution and the inner ones 13cm. Outer is ~2.4x the inner and one would expect the speeds to follow suit.

The post above yours explains why not all drives have such a drop, but they're essentially underrated as such.
 

primetime

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Messages
6,190
On 3 Seagate IronWolf drives, which have similar specs, show a dip of 55MiB/s, this is some 25% dip.

Here we are talking of a 120MiB/s dip, a 50% dip.
my Seagate enterprise drive does the same thing......and its completely normal (since mine is over half full now)
 

mwarps

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I'm pretty sure that every hard drive ever made exhibits this behavior. Welcome to spinning rust.
 

drescherjm

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Here we are talking of a 120MiB/s dip, a 50% dip.
50% is very normal and expected. Most drives will be around 1/2 as fast at STR on the inner tracks versus the outer tracks. I have seen this behavior first hand for 20+ years and hundreds of drives.
 
Last edited:

defaultluser

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Right, rotational media with fixed speed will always have a greater transfer rate on the outside edge.
 

ryan_975

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I'm pretty sure that every hard drive ever made exhibits this behavior. Welcome to spinning rust.
Every hard drive since since the 90's (maybe late 80's) when manufacturers started using zoned bit recording. Before that bit frequency was constant but bit spacing was variable, so transfer rates were constant, but upwards of half the recordable surface area was wasted.

Incidentally, ZBR is also why you can't low level format the surface anymore ("fdisk" and "format C:" is not low level formatting).
 

Luke M

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Apr 20, 2016
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Every hard drive since since the 90's (maybe late 80's) when manufacturers started using zoned bit recording. Before that bit frequency was constant but bit spacing was variable, so transfer rates were constant, but upwards of half the recordable surface area was wasted.

Incidentally, ZBR is also why you can't low level format the surface anymore ("fdisk" and "format C:" is not low level formatting).
Low level formatting is still a thing on SAS drives, for changing sector size. See:

https://forums.servethehome.com/index.php?threads/how-to-reformat-hdd-ssd-to-512b-sector-size.4968/
 

drescherjm

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Last year on an old XP system (not upgradeable / medical imaging device) I had to deal with low level formatting on some SAS drives that I purchased that had 520 byte sectors. The raid card rejected the drive until I had changed the sector size back to 512.
 
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