-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 On 01/20/2014 09:34 PM, Paul Wise wrote:
> On Tue, Jan 21, 2014 at 1:22 AM, Holger Levsen wrote: > >> wait, what? Do you have any vendor statements to support this 20% >> extra space? > > Flash is basically probabilistic storage and you need extra space to > ensure that the probability your data is stored remains high, That doesn't match my understanding, and I don't see anything to support it in the reference links you gave. My understanding is that flash is unreliable in that individual flash cells will die (cease to retain what is written) after "too many" write/erase cycles, where the value of "too many" goes down as the fabrication process gets smaller. To mitigate the real-world effect of this and extend drive life, manufacturers build in more flash than the reported drive capacity, a practice known as "overprovisioning". Modifying the drive firmware can make it possible to access this flash as normal storage, at the cost of drive lifetime. The reference links you provided do state that flash memory is "inherently unreliable and unpredictably fragmented", and one of them also states that a large fraction of the memory on any given flash die is likely to be bad sectors, but nothing I've noticed in them supports the claim that there's anything probabilistic about it. I do find one research-paper PDF, by a Google search, which describes techniques for allowing writes to flash memory at lower voltages than otherwise required; one of those techniques involves writing the data to multiple places in the hopes that at least one place will take the write, but there is no indication that this technique is widely enough used to justify the generality of the statement, and in any case that would be an implementation detail rather than a basic fact of flash memory. Is there something I've missed? - -- The Wanderer Secrecy is the beginning of tyranny. A government exists to serve its citizens, not to control them. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.15 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iQIcBAEBCAAGBQJS3nbMAAoJEASpNY00KDJrsz0QAJyCtXzYVRTAsnbH3QxX3D+t gk39FC0cqsJWrkV5/ZkQ3BEdFzELFRF39VbvDvterj0kfD1r8OMU9QmNu/xtv89s o9ZL1uYtZO/NTOoVXIDqpXJSsEfvyyajGjAEcyOprn+e7t2V+PkVaPCatiB/ikr4 8flpSjxiy+QfRByBzvIO4u0MySEfjRxZLlrslN184u/96mkwATjkwh2buRrQA/ZG pivJFRRfPXGBxg5tpyonOw5rvxelTw8f7rXZJxnuQyDxDnFSwKro6wl091F3Yfra h0PW/oR53h8sE2hV0F/NggfrqiDypXFJX1cm0AugyGbmsKTZ6VU9hB/uY1cc17H1 V5xauehyseFWFo85jKw4UF+i9BhkzCDt2jkiAGAsuWU1+rr8BiEBUsIQnRzizlmL YShCzFteFJmP1hxXqBhdFmMlMXsnS5o8Lb1QXNBX/Vsx4isB1AajTrL8DUASxR5I yz0WmDFbU5PVy0hwg+xKBebv/Vl30974MQwj3yvBGiLH/NZ3oJZZYD13ofqlyemA PKafQngtJ2zx//PJxrGiWWqvclkj1nbYwgSsc/dna3+B6XjmCwZ3ForCFFpOVgdj agLzB3CN3xnXjrJTKxZwMzpBgzLYHxMLZ8aKn0RWdS4A9OPUsvJTJmUfCIJh8yeD hnXXMmiCdHG4gpC7d4Qn =Cn+O -----END PGP SIGNATURE----- -- To UNSUBSCRIBE, email to debian-devel-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/52de76cc.1000...@fastmail.fm
