[Info-vax] VMS and the (lack of the) TRIM facility.

[JF Mezei]

On 15-06-25 16:42, Stephen Hoffman wrote:

> FWIW... DSE writes are unnecessary on any recent SSD, as — like the old 
> DSSI drives of yesteryear — most any recent SSD drives include an 
> secure erase command.

Spinning rust is analogue. The head outputs a analogue voltage and logic
decides if it is a 1 or 0.  The NSA types read that analogue signal and
based on the signal that should be obtained for current data, can deduct
what magnetic leftover from the previous write there is.

Hence the need to write multiple times, preferably random sequence to
prevent the NSA types from recovering the data.

However, does that principle work for flash ?

Since flash is digital, and since flash has to zap a page before it can
be written to, is is even possible for NSA types to try to figure out
what was written at a block/page before current data was written ?

The whole idea of writing data/zeroes over a block in SSD becomes moot
if that data is not actually erased but rather copied from page to page
as each write is done, leaving the original untouched.

TRIM marks the block as free and when all blocks in a page are free, the
page can be zapped and become available. But it isn't clear to me that
you can zap data, unless the SSD has a built-in function to zap a page
clean.