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SSD read speed slower than HDD?
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SSD read speed slower than HDD?

I have tested read and write speed with dd and result is:
SSD write:

dd if=/dev/zero of=/root/testfile bs=100M count=1 oflag=dsync
1+0 records in
1+0 records out
104857600 bytes (105 MB) copied, 0.252533 s, 415 MB/s

HDD write:

dd if=/dev/zero of=/root/testfile bs=1M count=1 oflag=dsync
1+0 records in
1+0 records out
1048576 bytes (1.0 MB) copied, 0.00765029 s, 137 MB/s

SSD read:

dd if=/root/testfile of=/dev/zero bs=100M count=1
1+0 records in
1+0 records out
104857600 bytes (105 MB) copied, 0.0786902 s, 1.3 GB/s

HDD read, I am including successive tests:


dd if=/root/testfile of=/dev/zero bs=100M count=1 oflag=dsync 1+0 records in
1+0 records out
104857600 bytes (105 MB) copied, 1.88679 s, 55.6 MB/s
root@vps:/dev# dd if=/root/testfile of=/dev/zero bs=100M count=1
1+0 records in
1+0 records out
104857600 bytes (105 MB) copied, 0.588729 s, 178 MB/s
root@vps:/dev# dd if=/root/testfile of=/dev/zero bs=100M count=1
1+0 records in
1+0 records out
104857600 bytes (105 MB) copied, 0.446045 s, 235 MB/s
root@vps:/dev# dd if=/root/testfile of=/dev/zero bs=100M count=1
1+0 records in
1+0 records out
104857600 bytes (105 MB) copied, 0.0489695 s, 2.1 GB/s
root@vps:/dev# dd if=/root/testfile of=/dev/zero bs=100M count=1
1+0 records in
1+0 records out
104857600 bytes (105 MB) copied, 0.0470945 s, 2.2 GB/s

According to this HDD reads better 1.3GB/s vs 2.2GB/s. Can you explain please?

Comments

  • oflag=dsync

  • DACDAC Member

    Hi cikatomo,

    You used different test method for each drive, the HDD was tested using oflag=dsync, which is why you get 4 results and each one is progressively faster. Try running oflag=dsync on the SSD and you should see the difference.

  • @DAC said:
    Hi cikatomo,

    You used different test method for each drive, the HDD was tested using oflag=dsync, which is why you get 4 results and each one is progressively faster. Try running oflag=dsync on the SSD and you should see the difference.

    It's the same result, with or without dsync

  • oneilonlineoneilonline Member, Host Rep

    Depends on the brand of the SSD? I've seen some that are real bad. So yea, I'm not surprised to see the HDD out perform.

  • What's the filesystem on the VPS and virtualization?

  • Are you clearing the filesystem cache and disk cache between tests?

    105MB is hardly a real test, your HDD probably has a 128MB cache, coupled with the OS file caching.

    Change the file test to 1GB and retest both

    Are you using the same filesystem on both? Or is one running some compressing filesystem eg ZFS

  • OP is clearly failing to clear the OS cache. OP's posted read speeds exceed SATA 3.2 limits.

  • another DD PORN

    Thanked by 1getvps
  • Meh, no cause to write dd in uppercase ...

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