Re: [gentoo-user] Recover on SSD

[Hinnerk van Bruinehsen <h.v.bruinehsen@fu-berlin.de>]

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On Mon, May 06, 2013 at 07:34:20PM +0200, Volker Armin Hemmann wrote:
> emm - no. Wear leveling does not need any spare blocks. A lot of drives
> do have spare blocks, but those are never the same size of the original
> size (at least not on drives you can buy for a sensible amount of
> money).  More like 120+8 or 160+16 or 256+16.
> 
> The spare blocks are used like on a hdd: some block goes bad, another
> one is mapped in.
> 
> Since the sdd firmware does not know if something was deleted or not* -
> it does know shit about filesystems**, you can of course dd an image, if
> you want to. Just like on a hdd.
> 
> *there are drives that do garbage collection without TRIM for fat and or
> ntfs.. so they seem to know a bit about filesystems.
> 
> ** and this is why TRIM exists in the first place. To tell the drive:
> yes, this data is gone. You don't need to care about it anymore.


The actual numbers were made up to make the point (maybe I should have
stated that in my OP). According to [1] they are normally between 7% -
37%.
Linux supports TRIM since Kernel 2.6.28. It's supported for several
filesystems (Ext4, Btrfs, FAT, GFS2 and XFS) but must be enabled via the
discard mount option. I don't have definitive information for Windows
but it seems to be supported by at least Windows 7 (as far as I can tell
without any user interaction).
Since the "deletion" happened under Windows I made a guess that it is
not totally unreasonable that dd may not work (if the deleted data would
have been "TRIMed").



[1] http://www.lsi.com/downloads/Public/Flash%20Storage%20Processors/LSI_PRS_FMS2012_TE21_Smith.pdf

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