On Wed, Dec 2, 2015 at 6:06 AM, Tinker <[email protected]> wrote: > In comparison, Karel's RAID1C in its present form would be like downloading > the file twice, and per-block CRC32 hashes twice, and then comparing both > copies to know you got the right thing. > > That's nice as it provides some automatic healing, but, that has a > limitation in the extra space used, and yet it's not safe to misdirected > writes, not even across the time that it's mounted continuously.
Seriously I do my best in order to increase data safety on OpenBSD based RAID1 system. What I see in practice looks good enough to me. > Just hashing the whole disk (and also keeping that hash in RAM fort he whole > period that it's in use) seems like a pretty inexpensive and "lean and mean" > way to data safety guarantees to me. I guess the devil is in "inexpensive". You again do your assumption based on what COW fss do. The problem here is that we're on completely different level and what's seems to be easy/inexpensive on COW fs level seems to be expensive on block-device level. At least I'm guessing from my own experience with SR-RAID. > We do know that what is happening is that disks do fail in all kinds of > ways, some less and some more incredible, we do see that ordinary > filesystems not would detect misdirected writes at the location where, and > the question I wanted to pose by this conversation was how to maximize data > safety - I think RAID1C is capable of detecting mis-directed write. I wrote about it in some of my previous email.
