I'm a fan of both PostgreSQL and SQL Server, but I think these numbers are very workload-specific. I've gotten 1GB/s throughput on SQL Server 2012 on spinning disks and CPUs older than the E5620, so I've no doubt that same workload would exceed 2GB/s on your hardware. The apples-to-apples comparison here is between the two versions of PG where the performance improvement is clear. It's harder to do an apples-to-apples comparison between PG and SQL Server because the optimal schema and queries for a particular workload are likely to differ for each of them.
With SQL Server I don't get 2000MB/s on the same hardware, more like 600-800MB/s. This is most likely because of LZ4 compression and large block sizes(64k-128k) on ZFS, that results in a lot less IO. Because with SQL Server, IO was the bottleneck.
So yes, it is very workload specific. For random read/write they are probably more similar. But for reading a lot of data that can be read sequentially, PostgreSQL seems to win hands down, because it can get a lot of help from ZFS compression.
I would love to run the same test when SQL Server is available on Linux. But ZFS do also deliver slightly better throughput and slightly more iops on the FreeBSD platform, which I ran this benchmark on. And SQL Server probably demands a 4k block size, which is so small that LZ4 compression has no effect as I've already tried to run SQL Server on ZFS via iSCSI.
Hmm, I've never run SQL Server on anything other than NTFS where 64KB was definitely the recommended block size. In either case, it's great to have choices. When the license fee is coming out of my pocket, I'm definitely not choosing SQL Server.
