On Thu, 12 Jun 2014 12:28:14 +0600 Roman Mamedov <rm@xxxxxxxxxxx> wrote: > On Thu, 12 Jun 2014 10:15:32 +0800 > Brad Campbell <lists2009@xxxxxxxxxxxxxxx> wrote: > > > On 11/06/14 14:48, Bart Kus wrote: > > > Hello, > > > > > > As far as I understand, md-raid relies on the underlying devices to > > > inform it of IO errors before it'll seek redundant/parity data to > > > fulfill the read request. I have, however, seen certain hard drives > > > report successful reads while returning garbage data. > > > > If you have drives that return garbage as valid data then you have far > > greater problems than what you are suggesting will fix. So much so I > > suggest you document these instances and start banging a drum announcing > > them in a name and shame campaign. That sort of behavior from storage > > devices is never ok, and the manufacturer needs to know that. > > If your RAM can return garbage, that's not a justification for having ECC RAM. > ECC RAM is a gimmick invented by weak conformist people. Instead, you should go > and loudly scream at the manufacturer who sold you that RAM! Errors from RAM > are never OK! RAM should always work perfectly! And if it doesn't, you have > greater problems. We shall not tolerate this behavior! So go get a drum and > start banging it as loudly as you can! Name and shame the manufacturer who > sold you that RAM. Fight the power, brother!!! Your screwdriver is leaking (*). Hard drives contain ECC. It should ensure undetected errors are an *extremely* rare event (more rare than bugs in the md code). If your ECC RAM started returning bad data without telling you, would you build a complex virtual memory system to load every byte from two different DIMMs into CPU registers and compare them before trusting them? I know that hard drives can return bad data. I've seen it happen. I don't think that trying to "fix" it in the md/raid layer is appropriate. File-systems and higher level data management systems (e.g. git) are much better placed to detect such errors than md/raid is. Supposedly btrfs will DTRT with your drives (though TRT is to RMA them, and I don't think btrfs has an RMA plugin yet). > > You can probably tell just how sick I am of reasoning like yours. That's why > we can't have nice things (md-side resiliency for the cases when you need/want > it), and sadly Neil is of the same opinion as you. > In general, if you want nice things you need to pay for them. If you are willing to pay I suspect you can find someone who is willing to provide. NeilBrown (*)http://www.zazzle.com/a_bad_analogy_is_like_a_leaky_screwdriver_tshirts-235102919981826183
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