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Re: [Nbd] maximum size of a read/write request

On 10/10/2011 03:00 PM, Folkert van Heusden wrote:
In practice, I'd try to avoid reads that are more than 1 MB minus
the reply header size, and writes that are more than 1 MB minus
the request header size.  qemu-nbd used to choke on those, though
the next release will only choke on more than 1 MB.

A good way to see what kind of request the kernel might make is
to use dd with the O_DIRECT flag.

That is too tricky: a new kernel version might show differnt
behaviour. Imho we should specify a limit or make it configurable or
put it in the protocol. We have 124 bytes of handshake left, we can
use 8 of them for a maximum blocksize.

O_DIRECT bypasses everything clever that the kernel might do.


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