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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