Any concerns with using a large diskio.coalesce_write_size?

Overall, from the description of coalesce, it sounds like it would be a good thing to set diskio.coalesce_write_size as large as possible to reduce hammering the disk (less often writes) and improve write performance (larger sequential writes).

With a fast download speed (20-100Mbit) and large disk cache (256-512MB) is there anything harmful about setting diskio.coalesce_write_size quite large?

Is there a limit to what could be considered useful? Does it stop doing anything after a certain point?

Could you theoretically set diskio.coalesce_write_size as high as your system will allow without throwing errors or causing other issues and have nothing to worry about?

Also as a related question, does uTorrent need to be restarted for a new diskio.coalesce_write_size to take effect or is the change instant?

Well, the less often you write data out to disk, the higher risk you run in potentially losing unwritten data to some kind of instability/crash.

http://forum.utorrent.com/viewtopic.php?id=44437

Setting the coalesced write size too high will probably result in this error. In fact, even a size of 4MB is already causing errors for many users (which is why it had to be lowered to 2MB default), so I wouldn't expect you to be able to set it too high anyhow.

Other than those 2 points, I don't see any inherent problems with increasing the write size. Whether it overrides the 2 minute limit in the disk cache, I'm not sure. Whether a restart is needed, I'm not sure either, but by my guess, it would.