Bitlocker, thread priority, and pause

stabar

New Member
Greetings, I have a few observations and a few suggestions for feature requests.

I'm running Eraser v6.1.0.2154 on Windows 7 Enterprise 64 bit. It is an HP EliteBook 8530p laptop with an intel Core 2 Duo CPU @ 2.53 GHz and 8 GB ram.

1) I just had bitlocker enabled a few weeks ago and I have noticed that there is a significant slowdown. I honestly don't have a before and after measurement, but would not be surprised if it is running about 25% slower. What would ultimately be the root cause of this slowdown? Yeah I realize there is an added layer of encryption due to bitlocker, but how convoluted does the process of overwriting a file become and what is the expected additional overhead? Is there any way to improve performance with bitlocker? Ie... blind writes versus first read (bitlocker:decrypt) then write (bitlocker:encrypt)?

2) When running, it appears like even though Eraser is consuming about 20% of the cpu, it is drastically impairing the response of normal system operations due to the high demand upon the hard drive; as expected. It is not unusual for some operations to take minutes before responding, such as CTRL-ALT-DEL. Generally I need to drop the priority of Eraser down to "Below Normal" in the task manager to regain usable control.
Feature Request: Have an option to set the priority, such as "Normal", "Below Normal", and "low" when it does run its tasks.

3) When running, it obviously hogs disk access that sometimes it can be a long wait to access certain resources reliably (such as a video).
Feature Request: It would be nice to have a Pause button to pause its operations. Could even have an option to allow it to pause when it finishes the current file. Another nice feature to pause, would be to specify for how long such as 30 seconds, 1, 5, 10, 30 minutes. That way you can do what you need to do and then allow Eraser to resume after the indicated amount of time.

Thanks! Great product and it is becoming highly stable on Win 7 64 compared to just a few months ago. Great work!
stabar
 

DavidHB

Active Member
I appreciate the constructive way in which you have put forward these ideas, and I hope that, when he finally gets back to the forum, Joel will feel the same.

I'd like to respond in a similar vein; before I can do so, please could you say whether the performance figures you quoted related to wiping free space or to erasing files/folders. If it was the latter, how large (approximately) was the group of files you erased, and what erasing method did you use?

The real resource issue with Eraser, in my opinion, is the way it monopolises available hard drive resources (both bandwidth and capacity), particularly when it is wiping free space. Personally, I wouldn't have the machine do anything else when a free space wipe is running; if I remember, I also pause or shut down background activities such as antivirus before I start the wipe.

David
 

Joel

Active Member
stabar said:
1) I just had bitlocker enabled a few weeks ago and I have noticed that there is a significant slowdown. I honestly don't have a before and after measurement, but would not be surprised if it is running about 25% slower. What would ultimately be the root cause of this slowdown? Yeah I realize there is an added layer of encryption due to bitlocker, but how convoluted does the process of overwriting a file become and what is the expected additional overhead? Is there any way to improve performance with bitlocker? Ie... blind writes versus first read (bitlocker:decrypt) then write (bitlocker:encrypt)?
I would think your gut feel is correct. Encryption is definitely slow -- usually a modern CPU should be able to manage AES-128 at around 120MB/s, but that's at 100% usage of a core. That doesn't take into account the overhead used by encrypting blocks, deriving keys etc etc. Whether performance can be improved, I won't be too sure, you may like to check with Microsoft (your business obviously has a Software Assurance contract with them, hence you can get Window 7 Enterprise...)

stabar said:
2) When running, it appears like even though Eraser is consuming about 20% of the cpu, it is drastically impairing the response of normal system operations due to the high demand upon the hard drive; as expected. It is not unusual for some operations to take minutes before responding, such as CTRL-ALT-DEL. Generally I need to drop the priority of Eraser down to "Below Normal" in the task manager to regain usable control.
Feature Request: Have an option to set the priority, such as "Normal", "Below Normal", and "low" when it does run its tasks.
The main bottleneck, as David correctly pointed out, is the I/O subsystem, not so much the CPU. I agree that in addition to point 1, coupled with Eraser using cryptographically strong pseudorandom data generation, CPU usage would be around 50% of one core. On a computer without disk encryption, I observe around 15-20% CPU use, mainly stuck in the crypto routines.

stabar said:
3) When running, it obviously hogs disk access that sometimes it can be a long wait to access certain resources reliably (such as a video).
Feature Request: It would be nice to have a Pause button to pause its operations. Could even have an option to allow it to pause when it finishes the current file. Another nice feature to pause, would be to specify for how long such as 30 seconds, 1, 5, 10, 30 minutes. That way you can do what you need to do and then allow Eraser to resume after the indicated amount of time.
That's really in the pipeline, but will only appear in 6.2

stabar said:
Thanks! Great product and it is becoming highly stable on Win 7 64 compared to just a few months ago. Great work!
Thank you for your support!
 

stabar

New Member
Thanks David for the additional questions and the deeper insight into challenges at hand.

The files that I erase are usually in groups of about 2 to 5 gigabytes and can be anywhere in the neighborhood of half a dozen to 20,000 or so files.

I tend to only use 1 pass pseudo random mode.

Oh wow... wait I think I found the problem: let me test it.

Yeah I found the cause of the slow performance! Right after installing Bitlocker I installed the latest nightly build of v6.1.x and it apparently (it must have, right? :) ) defaulted to the Gutmann 35 pass for the default file erasure method! Shows you how infrequently I browse the configuration settings! I should probably double check them after each update.

I set it back to the pseudo random 1 pass and it is back to its quick self.

So for the record, even with Bitlocker enabled, the single pass psedudorandom method is still very fast.

And yes, my two other suggestion could still be valuable.

Thanks David!
Stabar
 

DavidHB

Active Member
Thank you. At least I was right to ask you about the erasing method :) .

The default to Gutmann is a bit of an oddity. Joel, with some justification I think, believes that it's what users expect. But, as you clearly agree (as does Peter Gutmann himself), the method is gross overkill for ordinary users (those who could sensibly use freeware issued under the GPL Licence) and modern, high density hard drives.

David
 
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