On 09/12/2014 01:59 PM, Paul Gilmartin wrote: > On Fri, 12 Sep 2014 09:16:54 -0700, Anne & Lynn Wheeler wrote: >> re: >> http://www.garlic.com/~lynn/2014k.html#7 [sqlite] presentation about >> ordering and atomicity of filesystems >> >> part of the issue was that incomplete write ... with propogated zeros >> ... would also (then) rewrite the error correcting codes for the record >> (with propogated zeros) ... so there wouldn't even be an error >> indication that the write was performed incorrectly (installation >> wouldn't even know to perform restore because of write error). >> > It's almost as if they concealed the error on purpose. Well, not quite; > it depends on where in the data path the ECC was generated -- it > should have been done farther upstream. > >> later fba disks ... especially in conjunction with raid ... had >> requirement that single block write would complete correctly once >> started. ... >> > With what probability, and subject to what assumptions? If the > data lead to the write head fails mechanically at a critical time, a > bad block will be written. Negligibly improbable? Yes. Physically > impossible? No. Detectable by ECC? Probably. > > -- gil > > If the hardware knows it has incomplete information to write an entire block because of some abnormal hardware condition, then something should be done to guarantee that any later attempt to read that block will produce an error indication. If that is not the case, this would appear to be a violation of one of the major tenets of mainframe design: that any data errors resulting from hardware issues should be at least detectable, if not correctable. Writing a "valid" block with trailing zeros in such a case sounds a bad design decision.
-- Joel C. Ewing, Bentonville, AR [email protected] ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
