Re: NetBSD block vs raw disk I/O

[mlelstv%serpens.de@localhost (Michael van Elst)]

cryintothebluesky%gmail.com@localhost (Sad Clouds) writes:

>Reading from the virtual RAID drive gives throughput of 892MB/sec for
>raw device, but only 53MB/sec for block device. This is NetBSD-8

>Any ideas why block device I/O is so abysmal? Is this something
>specific to NetBSD?

When using the block device, everything is funneled through the
classic buffer cache. The buffer size is retrieved from the disklabel
and defaults to 2kbyte only. Finally, reads are done synchronously
without significant read-ahead.

This is specific to NetBSD, but it is hardly used because file I/O
is done by the virtual memory system, bypassing the classic buffer
cache. So there is no incentive to improve the situation as it also
requires a redesign of the buffer cache and some people would rather
get rid of the block device interface.

So, just don't use it. In particular not for benchmarks :)

-- 
-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."