On Wed, Dec 2, 2015 at 10:39 AM, Tinker <[email protected]> wrote: > On 2015-12-02 17:31, Karel Gardas wrote: >> >> I think RAID1C is capable of detecting mis-directed write. I wrote >> about it in some of my previous email. > > > Hi Karel, > > I'll follow up on the other things in a separate email later, but, you > clarify that you think RAID1C has protection against misdirected writes > already - I don't understand how it works, can you please explain to me > *exactly* how it can be said to be solid against misdirected writes?: > > > Let's assume the following nightmare scenario: > > * You write data to sector X. All the physical writes for that on all the > underlying disks are mis-directed (about 4 writes).
I've been talking about mis-directed write (singular!) while you suddenly switch to talk about writes (plural!). So what you describe here is basically you get *all* writes to *all* drives mis-directed? Oh, what's the probability of this? Well, if your read on the drives is not mis-directed in the same way (why would we then be talking about mis-directed write right?), then you read old data from the sector silently. BOOOM! :-) But allow me to counter with the question: what will your scheme do if *all* writes to *all* your drives are mis-directed? Wouldn't it also return old data on read from X? :-)
