Slow external hard drives (Seagate Backup Plus and WD My Book)

Discussion in 'Mac Accessories' started by Narial Taster, May 25, 2015.

  1. Narial Taster macrumors member

    May 17, 2011
    I have a 4TB Seagate Backup Plus drive and recently bought another one to back it up. The drive that arrived (another Backup Plus) was exceedingly slow during data transfers; it would show copy times for a 2 something TB folder in days and then stall. I reckoned that I'd gotten a faulty drive and asked for a replacement, which behaved the same way. I then replaced it with a WD My Book 4TB. All the data copied over ok but I've noticed that the WD has taken a huge hit in speed after the data transfer. A Blackmagic Disk Speed Test comparison showed the read and write speeds go from around 150 MB/s when the drive was empty to around 70 MB/s when I had transferred everything over (225 GB of free space was remaining at this point). Surprisingly, the original Seagate drive (the one that works fine), which has the exact same data on it, doesn't show such a drop in speed and clocks in at around 120 MB/s for both the read and write speeds. My questions are:

    1 - Is such a drastic drop in speed (from 150 MB/s to 70 MB/s) normal when a drive fills up or could the WD drive be defective and I should ask for a replacement?

    2 - Could I be doing something wrong while formatting the drives? I use Disk Utility to do a simple Mac OS Extended (Journaled) format and don't use the WD turbo or other such drivers. I've been doing this for years and am only asking as I am surprised at the number of drives I've faced issues with this time.
  2. ColdCase macrumors 68030

    Feb 10, 2008
    Try a different USB cable and Mac port.

    How did you copy the files? Select all and then drag/drop. Or did you do some individual folder drag/drop and have several parallel tasks going on?

    Typical hard drives will slow down after say 50% full but that depends a lot on seek times and "fragmentation" like characteristics. If the OS has to spend some time finding empty sectors, its going to take some time, and advanced format drives do something like 4K blocks.

    Modern eco drives will sometimes throttle throughput after some period of steady writes.

    Many of these kinds of issues are cable/connector related, error rates go sky high.
  3. Narial Taster thread starter macrumors member

    May 17, 2011
    Thanks for looking into this, ColdCase. I did as you suggested and tried the USB 3.0 cable that came with my Seagate drive and the speeds remain the same (Although the read and write speeds on the WD went down to 35 MB/s on one test. However, I wasn't able to replicate this and all subsequent tests came out around the 70 MB/s mark.)

    I first copied over a 2+ TB folder and then initiated copy on five more folders that cumulatively came in at 1+ TB. I let the data transfer complete overnight and ran the speed tests after the transfer process was completed. Does the way in which the data was transferred impact the speed of the hard drive? What is the best way to transfer large folders?
  4. LiveM macrumors 65816


    Oct 30, 2015
    It is normal for it to slow up as it fills and this should be in the manual. It has to start putting things across different parts of the disk platter.

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3 May 25, 2015