Re: RAIDframe performance vs. stripe size

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

> In general it won't access just one filesystem block.
> It will try to readahead 64KB
Oh, so this declustering seems to make matters even more
complicated^Winteresting.

Staying with my example of a 16K fsbsize FFS on a 4+1 disc Level 5
RAIDframe with a stripe size of 4*16k=64k:

Suppose a process does something that could immediately be satisfied
by reading one fs block (probably it matters whether that's a small file,
a small portion of a large file, a small directory, a portion of a large
directory, inodes, free list or whatever?). Now, if that, as I understand,
always causes FFS to in fact issue a 64k request to RAIDframe, this would
need to read a full stripe and so need all but one disc. So it can't be
parallelised with another process' request, can it? Does this mean I'm better
off with a stripe size of 4*64k if I'm after low latency for concurrent
access?