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You are here: MacNN Forums > Hardware - Troubleshooting and Discussion > Mac Notebooks > Data Recovery on an SSD/TRIM Enabled Mac

Data Recovery on an SSD/TRIM Enabled Mac
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l008com
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Nov 4, 2014, 01:00 AM
 
I have a customer that wasn't me to try to recover some files he accidentally deleted. There are plenty of apps that can scan "empty" hard drive space for deleted files, Data Rescue is my app of choice. HOWEVER I was informed that he has a MacBook Air. Now assuming that is is not the original model with a 1.8" HDD in it, it would be running an SSD drive with TRIM enabled. He also told me that he had used the computer for a while (didn't specify how long a while is) after emptying his trash. So, does this mean that the data is almost certainly gone? TRIM would have flipped all those bits back to zero long ago, right? And an app like Data Rescue will find not a thing in the free space?

This TRIM stuff just occurred to me while I was thinking about how I can pretty easily recover every jpg I can find in the empty space, then run some kind of filter to put the ones over a certain resolution into a folder, and that can be his "possibly photos" folder that he could go through.

Why do people out there still not back up
     
reader50
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Nov 4, 2014, 01:25 PM
 
TRIM doesn't auto-wipe unused space. It allows the SSD to not copy the affected blocks when it resets a region internally. If no data has been written "nearby" the target data (within the same SSD logical block), then the deleted data can still be there. Unfortunately, there's no way to tell from the outside how the SSD is managing it's internal layout.

Retrieval chance goes down with the passage of time, goes up if the drive has a high percentage of free space. The only way to know is to try the retrieval.
( Last edited by reader50; Nov 4, 2014 at 01:39 PM. )
     
Mike Wuerthele
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Nov 4, 2014, 02:04 PM
 
Data recovery is more a function of drive's free space, and time used after data loss. In the former, the greater the space, the higher the chance of recovery. With the latter, the more time that has elapsed, the lower the chance of recovery.

In my (somewhat limited) experience, recovery rates between drives, be they platter or SSD, are about the same all other factors equal.
     
l008com  (op)
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Nov 4, 2014, 03:53 PM
 
reader50: Interestingly, I emailed ProSoft with this same question, about TRIM killing deleted file recovery. They said that yes, TRIM does erase deletes files when you empty the trash, so that a deleted file scan most likely will find nothing. Everyone one I ask about this seems to have a different opinion, I guess we'll have to wait and see.
     
l008com  (op)
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Nov 4, 2014, 08:49 PM
 
I just heard back from drive-savers and they said the same thing. TRIM is going to erase the data so it will most likely all be unrecoverable. What a bummer. Can you believe there are still people that don't back up at all!!!
     
P
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Nov 5, 2014, 07:21 AM
 
Well, OK, but...

TRIM doesn't really matter here. The only situation where it matters is if he used to have 100 GB stored, with the important data right at the end (added last), deleted say 50 GB of it and has since only filled up 25 GB. Then the data would be around without TRIM (and on a spinny disk), but won't be around now. In all other situations, it doesn't matter.

The reason is the same as the reason why TRIM isn't all that important. What TRIM does is send a command to make a certain logical block of storage "free", so it doesn't have to be maintained in the reshuffling of physical space and can be used for the load balancing again. The thing is that the file system driver is designed to reuse logical blocks from the bottom, so unless you now store significantly less data on your drive than you did when it was as full as it ever got, TRIM doesn't matter - whatever blocks you cleared will soon be reused, and the TRIM command was just waste of an op.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
   
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