Hi Chris, I sat on my reply for a day so I could make sure my response was suitably professional. On 01/24/2014 03:54 PM, Chris Murphy wrote: > > On Jan 24, 2014, at 12:57 PM, Phil Turmel <philip@xxxxxxxxxx> wrote: > >> On 01/24/2014 02:32 PM, Chris Murphy wrote: >>>>> So a URE is either 4096 bits nonrecoverable, or 32768 bits >>>>> nonrecoverable, for HDDs. Correct? >>>> >>>> Yes. Note that the specification is for an *event*, not for a >>>> specific number of bits lost. The error rate is not "bits >>>> lost per bits read", it is "bits lost event per bits read". >>> >>> I don't understand this. You're saying it's a "1 URE event in >>> 10^14 bits read" spec? Not a "1 bit nonrecoverable in 10^14 bits >>> read" spec? >>> >>> It seems that a nonrecoverable read error rate of 1 in 2 would >>> mean, 1 bit nonrecoverable per 2 bits read. Same as 512 bits >>> nonrecoverable per 1024 bits read. Same as 1 sector >>> nonrecoverable per 2 sectors read. >> >> I don't know what more to say here. Your "seems" is not. > > Please define "bits lost event" and cite some reference. Google > returns exactly ONE hit on that, which is this thread. If we cannot > agree on the units, we aren't talking about the same thing, at all, > with a commensurately huge misunderstanding of the problem and thus > the solution. I am not trying to define terminology, nor do I intend to. I have been paraphrasing and rephrasing in an attempt to help you understand the published terminology. It's hardly surprising that this thread is the only hit. As this list is *the* reference for linux raid technology, and is a reference for raid technology in general, I hope this helps future googlers understand the issue. > So please to not merely respond to the 2nd paragraph you disagree > with. Answer the two questions above that paragraph. The paired questions simply restated my previous answer with a few substitutions. I skipped what I presumed was a rhetorical form, and replied to your commentary in answer to the whole. > If the spec is "1 URE event in 1E14 bits read" that is "1 bit > nonrecoverable in 2.4E10 bits read" for a 512 byte physical sector > drive, and hilariously becomes far worse at "1 bit nonrecoverable in > 3E9 bits read" for 4096 byte physical sector drives. It is only hilariously far worse in *your* mind. > A very simple misunderstanding should have a very simple corrective > answer rather than hand waiving and giving up. I'm sorry if you think my attempts to teach have been hand-waving. I'm giving up. I can't help you further. Regards, Phil Turmel -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
