> 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?