2 bonnies can stop disk activity permanently

[Fluffles.net]

Hi Bruce,

I'm the "veronica" Arne mentioned in the freebsd-fs mailinglist.
Regarding the effectiveness of a higher blocksize, these are my findings:

areca RAID5 (8x da, 128KB stripe, default newfs, NCQ enabled)
              -------Sequential Output-------- ---Sequential Input--
--Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block---
--Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU 
/sec %CPU
ARC8xR5  8480 119973 91.3 247178 58.6 67862 17.5 90426 86.9 172490 24.0
120.7  0.5

areca RAID5 (8x da, 128KB stripe, 64KB blocksize newfs, NCQ enabled)
              -------Sequential Output-------- ---Sequential Input--
--Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block---
--Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU 
/sec %CPU
ARC8xR5  8480 128920 97.8 265920 58.9 116787 31.0 103261 97.8 392970
53.8 119.8  0.6

As you can see, the block read increased from ~172MB/s to ~392MB/s,
quite significant increase. Also the reqrite speed increased from
~67MB/s to ~116MB/s.

Ofcourse these tests are on a brand clean filesystem, which might not
tally with real-life crowded filesystems. But at least there is much
potential in a higher blocksize, and it would be a shame for it to crash
FreeBSD. There are quite a few people who store big files on big RAID
arrays; they could profit from a non-crashing FreeBSD with bigger
blocksize. Besides, a crashing VFS/Geom isn't all that sexy. ;-)

- Veronica