Re: IOCache vs. block cache

Ingo Weinhold wrote:
> On 2010-06-17 at 20:23:55 [+0200], Rene Gollent <[email protected]> wrote:
>> A question - what cases would the block cache actually used in? It
>> seems as if the file / IO caches cover the cases of actual file data,
>> which would seem to only leave things like FS metadata blocks going
>> directly through the block cache.  And even that seems somewhat
>> redundant if the IOCache is also at the device level. Am I missing
>> something?
> 
> It is FS dependent whether file and/or block cache are used. Unlike the 
> IOCache, which is a fully transparent write-through cache, both provide a 
> public API for the FS. The block cache is transactional. Blocks of committed 
> transactions are written with delay.

OK, so I assume the IOCache works at the device level, regardless of the FS?

I'm still confused about the difference between the file and block 
cache, or more specifically why the file cache offers an advantage over 
the block cache which is presumably a lower-level abstraction.

Simon

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