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Re: systems hangs with slow disk - how does FS locking work?

> My assumption is that the "big" data block written is devided in
> several small chunks (disk blocks, 512 bytes), which will then be
> written to disk sequentially, and with the system preempting if
> there's other work to do.  The preemption would further delay the
> writes, but write speed not an issue.

Depends.  Does the driver do DMA, or does it have to go with PIO?

If PIO, you may actually not be blocking all of userland for the whole
duration, but it may be getting only tiny amounts of CPU in between
each underlying transfer and the next, which may look very similar.

Especially if the PIO is slow.

Another possibility is that the underlying hardware uses a block size
larger than 612, like 2K or 4K, and is doing a read-modify-erase-write
cycle for each 512-octet sector.  Erases can be slow.

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