Hi Ashish, On 14/03/16 12:31, Ashish Pandey wrote:
Hi Xavi, I think for Systematic erasure coded volume you are going to take fragment size of 512 Bytes. Will there be any CLI option to configure this block size? We were having a discussion and Manoj was suggesting to have this option which might improve performance for some workload. For example- If we can configure it to 8K, all the read can be served only from one brick in case a file size is less than 8K.
I already considered to use a configurable fragment size, and I plan to have it. However the benefits of larger block sizes are not so clear. Having a fragment size of 8KB in a 4+2 configuration will use a stripe of 32KB. Any write smaller, or not aligned, or not multiple of this value will need a read-modify-write cycle, causing a performance degradation for some workloads. It's also slower to encode/decode a block of 32KB because it might not fully fit into processor caches, making the computation slower.
On the other side, a small read on multiple bricks should, in theory, be executed in parallel, not causing a noticeable performance drop.
Anyway many of these things depend on the workload, so having a configurable fragment size will give enough control to choose the best solution for each environment.
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