SAN stands for Storage Area Network. Working in the industry, you may have encountered NAS (Network Attached Storage) as well. How exactly is that different, and how is it relevant to us?
It's subtle, but important. While both introduce networked storage, only a SAN grants direct block-level access, as if the allocation were raw, unformatted disk space. NAS systems operate one level higher, providing a fully formatted filesystem such as NFS or CIFS. This means our PostgreSQL database does not have direct control over the filesystem; locks, flushes, allocation, and read cache management are all controlled by a remote server.
When building a highly-available server, raw I/O and synchronization messages are very important, ...