CD9660/md(4)/UFS22 silly behaviour

[Kostik Belousov]

On Sun, Jan 08, 2012 at 10:21:50PM +0000, Poul-Henning Kamp wrote:
> 
> I'm doing som data-mining on a pile of ISO images right now.
> 
> I stuck the ISOs on a UFS2 on a flash-disk for speed, and mdconfig(8)'d
> them so I could mount them.
> 
> The traffic pattern his "interesting":
> 
> dT: 1.003s  w: 1.000s
>  L(q)  ops/s    r/s   kBps   ms/r    w/s   kBps   ms/w   %busy Name
> [...]
>     1    733    733   1466    1.3      0      0    0.0   98.2| md39
>     1    733    733  23449    1.3      0      0    0.0   93.2| da0
> 
> Notice the 1:16 ratio on kBps but 1:1 ratio on ops/s ?
> 
> da0's UFS2 has 32k block-size:
> 
> 	magic   19540119 (UFS2) time    Wed Jan  4 16:41:47 2012
> 	superblock location     65536   id      [ 4f046cf5 c30697ee ]
> 	ncg     104     size    19537685        blocks  19228156
> 	bsize   32768   shift   15      mask    0xffff8000
> 	fsize   4096    shift   12      mask    0xfffff000
> 	[...]
> 
> It looks like every 2k read from CD9660 turns into a 32k block
> read in the UFS filesystem, without any beneficial caching happening.
> 
> Less than optimal I'd say...
> 
What is the access patern ? Is it random access, or sequential read
(from the cd9660 POV) ?
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