I was recently working with a distributed database running on Centos 7.2.Nodes for the DB were backed by a SAN, the SAN was reporting massive read/write volumes that did not correspond to the volumes read/written by the DB itself.It turns out the readahead buffer was far too large:# blockdev --getra /dev/mapper/mpatha18192Block size was 512 bytes.Updating that buffer to 128 had a drastic impact on the read performance, which I understand. But it also drastically reduced write volumes (by the same factor as read volumes basically).Can anyone explain how that could be the case? I have a fairly limited systems knowledge.
How could readahead buffer size impact write volumes?
centos;io;disk;cache