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.
