On Thursday February 22, [EMAIL PROTECTED] wrote:
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>
> hello,
> looking at your patches i was trying to understand patch-J-r5align
> does it mean that that particular request is not handled by the
> stripe cache?
Yes. A request that is not properly aligned cannot be handled by the
stripe cache. I'm not certain exactly what will happen, but I suspect
that it would mostly work but would occasionally cause data corruption
if a differently aligned request for a nearby stripe were written at
the same time. Occasional corruption is not something that I want!
>
> besides printing the warning (wouldn't it be better to print it only once
> or once in a while, instead of at every request)
Arguable it would be better to rate-limit the printing of the message,
but really, I don't want anyone to use raid5 in a situaiton where
requests might not be aligned, and I want them to get a very clear
message this it doesn't work.
>
> anyway once you properly configure your LVM system, misaligned requests happen only
> during vg operations, which are rare.
But even once is too often if it could corrupt your data.
I don't know much about the details of LVM, but if you can create
partitions that are not on a 4K boundry in the real device, then you
could certainly create a situation with lots of misaligned requests.
I hope to remove this restriction eventually, but until then, I want
people to be able to know when potentially bad things are happening.
NeilBrown
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