Head to head comparisons

The reason this section exists is that the most useful storage comparisons cross a vendor boundary, and vendors will not cross it. Synology will happily explain SHR. It will not put SHR next to ZFS RAIDZ2 for your exact drives and tell you which one leaves you with more space. A ZFS-flavoured tool will not tell you that on mixed drive sizes SHR wins outright, because ZFS truncates every member to the smallest drive and strands the rest.

The headline finding, stated plainly: with identical drives, Synology SHR is exactly RAID 5 and gains you nothing. Not roughly the same, exactly the same, because SHR with matched drives collapses to a single RAID 5 parity group. The advantage appears only when your drives differ in size, and it grows as they diverge. It also appears later, when you upgrade, because SHR is the only consumer scheme where replacing two of four drives with larger ones gains you anything at all before the fourth is replaced. That comparison is here, worked through band by band.

The other comparisons follow the same shape. Real numbers, a table near the top, an explicit verdict per reader type, and a plain statement of what you give up in each direction. RAID 5 against RAID 6 comes down to rebuild exposure rather than capacity. 2.5GbE against 10GbE comes down to whether your array can feed the link at all, because a single 7200 rpm drive sustains 150 to 260 MB/s and already saturates gigabit. NAS against cloud is the one where the honest answer is that they are complements: the cloud makes an excellent copy three and a poor copy one.

Where a comparison depends on a figure that changes, we say what the figure is and where it came from. Where it depends on a manufacturer specification we cannot verify, we leave it out rather than estimate it. Run your own drive set through the RAID capacity calculator before acting on any of it, because the right answer changes with your specific drives.