On 10/06/2011 12:53 PM, Folkert van Heusden wrote:
Hi, What is the maximum size of a read/write request? E.g. how much data can be requested/transmitted using one read or write command? And can this be limited using a nbd-client command-line setting and/or nbd protocol handshake?
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.
Paolo