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On 06/05/2013 20:36, Hinnerk van Bruinehsen wrote: |
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> On Mon, May 06, 2013 at 07:34:20PM +0200, Volker Armin Hemmann wrote: |
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>> emm - no. Wear leveling does not need any spare blocks. A lot of drives |
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>> do have spare blocks, but those are never the same size of the original |
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>> size (at least not on drives you can buy for a sensible amount of |
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>> money). More like 120+8 or 160+16 or 256+16. |
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>> |
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>> The spare blocks are used like on a hdd: some block goes bad, another |
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>> one is mapped in. |
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>> |
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>> Since the sdd firmware does not know if something was deleted or not* - |
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>> it does know shit about filesystems**, you can of course dd an image, if |
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>> you want to. Just like on a hdd. |
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>> |
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>> *there are drives that do garbage collection without TRIM for fat and or |
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>> ntfs.. so they seem to know a bit about filesystems. |
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>> |
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>> ** and this is why TRIM exists in the first place. To tell the drive: |
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>> yes, this data is gone. You don't need to care about it anymore. |
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> |
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> |
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> The actual numbers were made up to make the point (maybe I should have |
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> stated that in my OP). According to [1] they are normally between 7% - |
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> 37%. |
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> Linux supports TRIM since Kernel 2.6.28. It's supported for several |
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> filesystems (Ext4, Btrfs, FAT, GFS2 and XFS) but must be enabled via the |
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> discard mount option. I don't have definitive information for Windows |
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> but it seems to be supported by at least Windows 7 (as far as I can tell |
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> without any user interaction). |
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> Since the "deletion" happened under Windows I made a guess that it is |
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> not totally unreasonable that dd may not work (if the deleted data would |
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> have been "TRIMed"). |
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> |
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> |
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> |
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> [1] http://www.lsi.com/downloads/Public/Flash%20Storage%20Processors/LSI_PRS_FMS2012_TE21_Smith.pdf |
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> |
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A delete on an SSD is a very expensive operation, to my mind it seems |
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completely unreasonable to think that Windows would try and clear many |
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tens of GB just because it trashed a partition table. It would take |
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_hours_ to clear those blocks. |
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By far the easiest route would be to just do what is done for spinning |
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disks - write the partition table, leave whatever junk is in the cells |
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intact until the partition is formatted and actual data is written to |
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the fs. |
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As your results show, this is indeed what did happen. |
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-- |
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Alan McKinnon |
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alan.mckinnon@×××××.com |
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