On Thu, Oct 6, 2011 at 5:02 PM, Duddy, John email@example.com wrote:
As I understand it, Isilion is built up from "bricks" that have storage and compute power. They replicate files amongst themselves, so that for every IO request there are multiple systems that could respond. They are interconnected by an ultra fast fibre backbone.
So why not use gzipped files on top of that? Smaller chunks of data to access so should be faster even with the decompression once it gets to the CPU.
So, depending on your topology, it's possible to get a lot more throughput by working on different sections of the same file from different physical computers.
I haven't delved into BGZF, so I can't comment. My approach to block GZIP was just to concatenate multiple GZIP files and keep a record of the offsets and sequences contained in each. The advantage is compatibility, in that it decompresses just like it was one big chunk, yet you can compose subsets of the data without decompressing/recompressing and (as long as we actually have to write out the file subsets) can reap the reduced IO benefits of smaller writes.
That sounds VERY similar to BGZF - have a read over the SAM specification which covers this. Basically they stick the block size into the gzip headers, and the BAM index files (BAI) use a 64 bit offset which is split into the BGZF block offset and the offset within that decompressed block. See: http://samtools.sourceforge.net/SAM1.pdf