Copying to encrypted DMGs in Lion much slower than Snow Leopard

Question

LeoCastillo Author

Level 1

0 points

Copying to encrypted DMGs in Lion much slower than Snow Leopard

Hi guys!

I've been using Lion for a while, and love it.

However, I discovered what may possibly be a bug with encrypted DMGs.

I've made encrypted DMGs before to protect files. In Snow Leopard they worked well, just an like an unencrypted DMG.

However in Lion, it seemd that copying to encrypted DMGs is slower than molesses.

For example, I tried copying 10GB into a 20GB encrypted DMG. It reported it'll take 14 hours (yes HOUR not minutes) for the copy to succeed.

I know encryption would of course add some overhead, but in SL it was much much faster than this (possibly 15-20 minutes)?

Take note that the 10GB folder and the 20GB DMG are both located in the same hard drive; it's not being copied across USB/Firewire/Ethernet/Wifi.

It's a local copy.

Isn't that a bit strange? Do you guys experience the same thing? Or is there something wrong with my setup?

This is happening by the way in my 2011 MBP 15" with 8GB of RAM.

Would appreciate any thoughts.

Leo

MacBook Pro, Mac OS X (10.7.2), 2011 MBP

Posted on Oct 21, 2011 9:00 AM

Reply

Answer 1

OwenLars

Level 1

0 points

Dec 6, 2011 3:37 PM in response to LeoCastillo

Hi Leo

I am experiencing the same issue as you on my 2008 MBP running 10.7.2, so its not an isolated issue, defiently a bug.

All my older DMGs (created with Snow Leopard) are working fine, when i mount them in Lion i can copy files to them at decent speed. All my new DMGs (created with Lion) suffer from extremely slow write speed. I am not really sure if the read speed has also been affected, i havent tried to test that yet.

Based on the fact that my older DMGs still work fine, but not the new ones, I would guess its a bug that has been introduced with the Lion Disk Utility Application. There is something not quite right about the way it is creating the Blank Image File, and this is causing painfully slow write speeds to the image.

This needs to be fixed by Apple, its a fairly serious bug.

In the mean time i am wondering if there may be a way to "downgrade" the Disk Utility Application to an older version that actually works properly?

Reply

Answer 2

LeoCastillo Author

Level 1

0 points

Dec 6, 2011 5:50 PM in response to OwenLars

Thanks OwenLars. This thread has been out for so long without replies I was wondering if I was the only one.

Yes, I noticed the same thing too. Snow Leopard created encrypted DMGs work quite well, Lion created encrypted DMGs have slow writes.

A workaround I've been using lately is to duplicate an old SL created DMG, empty it and put in my new stuff.

A bug with Disk Utility makes sense. Hope Apple sees this thread and fixes it.

Reply

Answer 3

jsd2

Level 5

6,245 points

Dec 6, 2011 6:20 PM in response to LeoCastillo

Try creating an encrypted sparsebundle rather than an encrypted DMG. Copying items to a mounted sparsebundle image seems sigificantly faster, and sparsebundles are more efficient both in use of disk space and also with regard to the time needed to back them up when their contents change.

Reply

Answer 4

SeanLA

Level 1

0 points

Dec 28, 2011 2:27 PM in response to LeoCastillo

Same here -- very slow copy speed on encrypted DMGs created with Lion. I'm using the same workaround: duplicate SL DMG, empty it and add new files. Surprised there haven't been more Lion-ites with this issue.

Reply

Answer 5

motrek

Level 1

49 points

Apr 21, 2012 1:07 PM in response to LeoCastillo

I am absolutely seeing a problem with encrypted disk images.

I use encrypted DMGs on a USB flash drive. Worked fine with SL, but under Lion it takes *forever* to write anything to the DMG.

Activity Monitor shows tiny bursts of write activity but for the most part the drive seems to be completely idle when I'm trying to write to it.

Sometimes it can also take 2-3 minutes to unmount the DMG for no reason, i.e., again, the drive is not being read or written to, it just won't unmount.

Would be nice if Apple fixed this.

Reply

Answer 6

chaitatp

Level 1

0 points

Mar 16, 2013 12:55 AM in response to LeoCastillo

Hi

I am facing the same issue as you guys.

Encrypted DMG created with MacOSX 10.6 (Snow Leopard) works fine (fast). Move this Encrypted DMG to MacOSX 10.8 (Mountain Lion) still works fine (fast).

Encrypted DMG created with MacOSX 10.8 (Mountain Lion) works SUPER DUPER SLOW.

Still looking for a workaround.

Thanks

Reply

Answer 7

petermac87

Level 5

7,447 points

Mar 16, 2013 1:03 AM in response to motrek

motrek wrote:

Would be nice if Apple fixed this.

http://www.apple.com/feedback/macosx.html

Pete

Reply

Answer 8

Han73528

Level 1

0 points

Apr 27, 2014 7:42 AM in response to LeoCastillo

We are now on Mavrics and this problem still hasn't been solved!! Can we get a fix for this?

Reply

Answer 9

Sep 29, 2014 6:16 PM in response to jsd2

Creating an encrypted sparsebundle as jds2 suggested works for me. Copying a 1.5 GB file into a new, encrypted, sparseimage took over 4 min. Same file copied directly to disk, bypassing any disk image, only took 25 sec so I think that proves the disk hardware is fine. Same file copied into a new, encrypted, sparsbundle only took 30 sec. I don't understand why writes to a sparseimage are so incredibly slow, even in Mavericks.

Reply

Answer 10

cpragman

Level 2

465 points

Jan 30, 2015 9:09 PM in response to Tom Francais

Today I'm making a 150GB encrypted DMG on Yosemite. I couldn't believe how slow it was, and found this thread.

Filing a bug report now.

Reply

Answer 11

Aug 5, 2015 6:32 AM in response to LeoCastillo

Solution:

Create the encrypted DMG file. Eject if mounted, and copy the newly created, empty DMG file to an external HDD. Delete the original one on your desktop. Mount the DMG file from your external HDD onto your desktop, and copy the files you want to copy. Takes the expected amount of time (minutes, not hours!).

Hope this helps someone. (Lion 10.7.5)

Reply