When does `write' return 180
Andrew Xue It is not silly.
It depends on a coupla things. If you have much more than 1GBytes of ram, the write could return as soon as the data get to a memory buffer. Possibly some of the cache would have to be paged out, but not necessarily.
Andrew Xue Sorry. That was a DEC thing on their hard drives in the very late 1960s, at copy-on-write. Their...
It also depends if file fd is a raw file or not (if you are using raw file systems, you probably already know enough to answer your questions; so probably not a raw file). If it is, I believe you must wait until the write completes, but OTOH, you do not need to take the time to find system buffer space and copy from user space to system space, and you might be able to do it in a giant "spiral write" as DEC used to call it. Depends on hardware and the low level driver, I would expect.
And if you are really worried about the data getting onto the disk platter, consider that many drives have 8 to 16 MByte buffers inside, so even when the kernel thinks it has written to the hard drive, there may be up to 8 MBytes that might not get there at all if Murphy is on the job.
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