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Old August 13th 12, 02:17 PM posted to
Mark F[_2_]
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Posts: 164
Default Does TRIM support hurt data recovery?

On Mon, 13 Aug 2012 09:47:24 +0200, Dirk Munk wrote:

As you will know an SSD can only write or erase data, it can not rewrite
data. If a rewrite is necessary, the disk will first have to erase the
old data and then write the new data. That is very time consuming.

Normally when you delete a file, nothing very much happens. The
directory entry will be deleted etc. , but the data will still be there
until it is rewritten by other data. So in principle a unerase is possible.

We don't want this rewrite in an SSD, it would make the device very
slow. That is where the trim facility is used. Once a file has been
deleted, the SSD will get the information on where the file is on the
SSD, and it can then erase all the old data in the background.

The SSD will not wait until the space is really needed, that would be no
improvement over the normal rewrite procedure.

So, specifically, if TRIM is working, in general it will be impossible
to recover files deleted from the operating system, even by someone
with access to the drive internals and even if no further data is
written from the computer.

This has someone the same effect on data recovery as erasing files
immediately upon deletion has with spinning drives. (Of course,
you can't rely on the data being erased due to TRIM related activity,
but would seem to imply that you should power down any drive that you
accidentally deleted a file on as soon as possible after you notice
the error. This is contrasted with the case of spinning drives and
flash drives without TRIM support, where powered on time is not
a factor in data recovery as long as you don't write to the device.)

Mark F wrote:
Does TRIM support hurt data recovery?

For example, if I delete a file in Windows will the SSD drive's
TRIM support erase the data?

If I delete a partition, will the SSD drive erase all of the
data that was in the partition?

Does it depend on the SSD drive, or are things defined so as
to mean the data either, depending on the definition:
. always be erased eventually, even if no further writes are done
. never be erased unless the space is actually needed.

It seems to me that TRIM support in the operating system and the
device will mean that the data MAY be erased a before being needed,
but I don't know how much, if any, writing has to be done before the
drive can start erasing things.