Bitlocker encryption process ULTRA slow, solutions? RRS feed

  • Question

  • Hello forum,

    I recently got a 4 TB Western Digital HDD (Blue WD40EZRZ - mfg. date 2015) and started to encrypt it with Bitlocker. This was 50 hours ago. Now it sits at 69% and is still encrypting! At a speed of 34% a day I am going to have to wait another day before Bitlocker finishes the process.

    System specs: Win 10 pro 64 bit, ASRock 990FX Fatality Killer, AMD FX-8350, 16 GB RAM, OS on Samsung SSD

    I chose the new XTS-AES encryption method. Copying of large files from any system disk to the 4 TB disk and the other way around runs at 120-150 MB/s (seems normal to me).

    According to the Windows Taskmanager the Bitlocker process is using the drive at 100%, constantly reading off and writing on it at 7-15 MB/s

    I don't know about the mechanics of a consumer grade harddrive, but running at 100% for 75 hours (>3 days!) probably isn't going to improve its health.

    In the past, encrypting a whole drive with Bitlocker always took some time, but even with drives as big as 3 TB it had never taken more than 24 hours.

    Is this some kind of bug within Bitlocker? Is the disk particularly slow?


    Edit: I started encrypting a Western Digital 1TB (Blue WD10EZEX - mfg. date 2013) drive in an external USB 3 case and it is considerably  faster. The encryption process reads and writes at 50 MB/s, while the internal 4 TB disk still only encrypts at ~10 MB/s.

    Friday, January 8, 2016 5:10 PM

All replies

  • Hi,

    Generally, encryption, and this is regardless of the encryption soft used, averages about 100 GB/Hour on traditional hard drives of various types. With BitLocker, it has to encrypt every sector on the drive. A 1 TB 7200 RPM traditional desktop drive encrypts a bit faster if it is an internal drive, usually taking about 8 hours to encrypt. 5400 RPM or 2.5" traditional laptop drives take longer.

    There are also other variables, SSD's, even have to encrypt the whole volume, encrypt much faster than HDD.

    And if it is an external hard drive which uses USB 2.0, it would be even much slower.

    Windows 8.X and Windows 10, at least with BitLocker, break with tradition, and only require that the used space on the drive be encrypted. So with full data loaded hard drive, it takes much longer than empty one, and 4tb might take even longer than encryption time of four 1TB drives.


    D. Wu 

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    Monday, January 11, 2016 4:01 AM
  • There are several components involved, for example the mainboard's sata controller, which is not used for the external usb drive. So maybe it's some sort of performance bug with this hardware constellation, who knows. Or the controller driver is good at read/write (sequential), but not at the way bitlocker does it.

    Based on experience, I can say that Bitlocker performs good in encryption time. I'd expect to get 30-50 MB/s out of that drive, you get a lot less, well... what can you do. You'd have to run many tests to find out.

    Monday, January 11, 2016 1:53 PM
  • There are several components involved, for example the mainboard's sata controller, which is not used for the external usb drive. So maybe it's some sort of performance bug with this hardware constellation, who knows.

    That might be it. It might also have been the disk itself, which maybe isn't capable of reading and writing at high speeds at the same time - since it's only the the consumer grade Blue drive. I'll probably never know, since the encryption process finally finished after 3 and 1/2 days. Basically I wanted to report the issue that I had, for other to join in or for MS to address it, if they see that they can do anything about it.

    But one thing I know for sure: I am not going to reencrypt the drive anytime soon ;)

    Tuesday, January 12, 2016 8:28 PM
  • TL;DR:
    To get a 5x speed boost on encrypting your full drive in Windows 10:
     1. Enable Bitlocker in the running OS, but pause the encryption once it's in progress
     2. Create a recovery disk, boot it up, go to command line
     3. Resume encryption of the drive using "manage-bde -resume" while in the recovery environment
     (4. Pause again at 99% and go back to the running OS and finish it from there...? This is probably unnecessary, but this is what I did.)


    I just tried to encrypt my 2TB external HDD on the latest Windows 10 Pro using Bitlocker (entire drive, compatible mode), and since I only got to 3% within ~2 hours, I started looking into what was going on. I checked on Task Manager's Performance tab, and while CPU and memory was idling, disk usage on the affected drive was at 100% constantly. However, at the same time, it reported 10 MB/s read and also 10 MB/s write, which was very slow compared to how this drive performs when I read / write files myself. This is when I started searching the internet and found this thread.

    First I wanted to obtain a Windows 8.1 Recovery Disk, to try to boot it up and encrypt the drive from the command line tool "manage-bde", hoping that it would be a lot faster as reported here. However, I wasn't able to find an ISO for that recovery disk, so I gave up on that. But as a last effort, I decided to try the same with the Windows 10 Recovery Disk that I could simply create from my running OS. And the trick worked!

    Windows 10 Pro (same machine, same drive, same everything!), Running OS vs. Recovery Disk
    (I will just post the results in "percent per hour", as it shows the speedup just fine, but if you'd like, you can calculate MB/s.)

    === Encryption phase 1 - Running OS ===
    20:13 - 0.0%
    00:01 - 5.9% --> 1.553% per hour

    === Encryption phase 2 - Recovery Disk ===
    00:08 - 5.9%
    00:39 - 11.0% --> 9.871% per hour
    02:07 - 25.3% --> 9.750% per hour
    04:44 - 50.0% --> 9.439% per hour
    11:41 - 99.2% --> 7.079% per hour

    === Encryption phase 3 - Running OS ===
    12:10 - 99.2%
    12:41 - 100.0% --> 1.548% per hour

    === Results ===
    Running OS: average 1.55% per hour; estimated total 64.5 hours
    Recovery Disk: average 8.08% per hour; estimated total 12.4 hours
    SPEED UP: ~5x

    My guess is that Windows 10 is throttling the encryption process to a "safe speed" for some reason, probably to keep the system usable while it's working. You can see that the processing speed is approximately the same at the start (~0%) and at the end (~100%) when the OS is running, whereas it gradually slows as we get to the slower parts of the disk while encrypting in the recovery environment. So basically the disk IO is really maxed out in the recovery environment, while the bottleneck is somewhere else in the running OS.
    • Proposed as answer by Panther-D Thursday, June 16, 2016 12:16 PM
    Thursday, June 16, 2016 12:16 PM
  • There must be an easier and faster way to encript my 4TB Seagate external HD with a HP-6300 Pro PC, i5 processor. BitLocker is going 1% per hour, so it will take 100 hours to complete the process. It is incredible that Microsoft has not thought of a solution to this issue. I hope somebody can provide an alternate option that jumping to a recovery disk.



    It is incredible that Microsoft has not thought of a solution to this issue,
    It is incredible that Microsoft has not thought of a solution to this issue,
    Wednesday, July 26, 2017 10:50 PM
  • Thank you Panther-D,

    your post is very helpful.

    I tried it on Win 7, at the safe mode the encryption is running 5 times faster vs normal boot Win 7.

    Thank you for saving my time.

    Saturday, July 29, 2017 4:01 AM
  • On larger hard drives, encryption is slow, bitlocker corrupted my 3TB HD. I did backed up my data and then formatted the drive to get a clean start with bitlocker encryption on the entire HD. Encryption ran continuously for 2 days. When I finely I had to transfer my data back, this is where the encryption failed. The drive failed several times and then eventually got burnt, since its been running continuously for several days (encryption time and then data transfer time).

    Bitlocker encryption needs to improve on larger hard drives.

    Thanks Marcus.

    Saturday, November 4, 2017 11:05 PM
  • Great analysis, thanks!

    My speed was around 15 MB/s from within Windows 10, using new encryption mode.

    Additionally, I had very slow speeds on my 2 TB HDD when handling small files and especially when reading/writing to the same drive at the same time, but this was also partly true for large files.

    That caused system hangs and sometimes even very long shutdown-periods, as Windows still tried to write something to the HDD.

    In my case I thought it was a corrupt SSHD, which I sent back and bought a normal HDD - with similiar bad performance.

    Do you see any decrease in speed on your Bitlocker-system lately? (As if some Windows 10 update introduced a new "feature" which actually results in slow Bitlocker-drives.)

    Did you try to find any difference between new/old encryption mode?

    Sunday, September 23, 2018 2:15 PM
  • I personally Experienced 2 TB Drive took around 6 Hours Plus on Intel 7 Chip with 32 GB Ram.

    Mr D. Wu gave an Useful update


    Wednesday, December 25, 2019 12:29 AM