On 09/01/2016 02:48 PM, Alex Austin wrote:
CC'ing linux-scsi and linux-block.
Also, please CC me in replies.
On Thu, Sep 1, 2016 at 4:43 PM, Alex Austin <aaustin@xxxxxxxxxxxxxxxxxxx> wrote:
Hello,
What is the most performant way to directly interface with an attached hard
drive? I've so far used read()/write() on /dev/sd_ but I find error handling
exceedingly difficult, as I don't always even get errors reported, even if the
open() call includes O_DIRECT. I've also used ioctl(SG_IO), but find that it's
extremely slow due to the lack of queuing support in the API. Is there a
mid-level API that will get me decent error handling while allowing command
queuing, or do I just need to make multiple threads all doing separate SG_IO
ioctls?
What the most efficient way is to interface is with a hard drive depends
on the I/O pattern. Are you aware that buffered I/O performs read-ahead?
Have you already tried to tune the read-ahead setting (blockdev --getra
/ blockdev --setra)?
BTW, if you need an example of how to queue SG_IO, you are welcome to
have a look at the fio source code. You will probably be interested in
the bsg API. See e.g. https://lwn.net/Articles/174469/.
Bart.
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