Intermediate Home Server Setup: A $3,539 Four-Bay Build

This is the buy-once tier. Four bays, ECC memory, Synology Hybrid RAID, real network speed and a backup that matches the array, for about $3,539. The point of this build is not that it is the best specification for the money, because it is not. The point is that nothing on the list needs replacing in three years, and the one feature it has that cheaper hardware does not is the one that makes growing the array painless.

The drives are 52 percent of this build and the enclosure is 21 percent. Add the backup drive and storage media is 72 percent of the total. It is worth sitting with that ratio before reading any enclosure comparison, because the amount of attention the internet pays to NAS boxes is inversely proportional to their share of the bill.

What capacity do you actually end up with?

Four 12 TB WD Red Plus drives give 48 TB raw. What survives parity depends entirely on the layout, and this is the comparison no manufacturer tool will show you for the same physical drives.

Two things in that table are worth saying out loud. With identical drives, SHR and RAID 5 are exactly the same, and SHR-2 and RAID 6 are exactly the same. SHR is not a cleverer parity algorithm; it is standard Linux software RAID arranged so that mismatched drives can be sliced into bands. Give it four identical drives and it collapses into a single RAID 5 group. Anyone telling you SHR is inherently more efficient is describing the mixed-drive case without saying so.

Second, the capacities are decimal terabytes, the figure printed on the drive label. Your NAS reports binary tebibytes while still labelling them "TB". One TB is 1,000,000,000,000 bytes and one TiB is 1,099,511,627,776, a fixed ratio of 0.909495, which makes every number look 9.05 percent smaller. Nothing has gone missing. The TB against TiB chart has every capacity, and the RAID capacity calculator shows both units for any drive set.

Why pay the Synology premium at all?

Because of what happens in year three. Suppose you fill 36 TB and want more. The cheapest move is to replace two of the four drives with 20 TB drives rather than all four at once. Here is what each scheme does with 12, 12, 20 and 20 TB:

That is a 8 TB difference from the same four drives. Under standard RAID you would have spent roughly $1,600 on two large drives and gained nothing at all until you replaced the other two. SHR gives you most of it immediately. This, and not the software polish, is what the premium buys, and it is why the DS925+ earns its place here over hardware with a faster processor at the same price. The full band arithmetic is in SHR against RAID 5.

The corollary, stated fairly. If you always buy every drive at once and replace the whole set at once, SHR gains you nothing at any point, and hardware like the Asustor Lockerstor 4 Gen3 or a cheaper two-bay plus a bigger drive budget may serve you better. Be honest with yourself about which kind of buyer you are.

Should you run SHR or SHR-2?

The trade is 12 TB of capacity for a second drive of parity. At 12 TB per drive that is a genuine decision rather than an obvious one, and it turns on rebuild exposure rather than on failure rates.

When a member dies under single parity, the array reconstructs it by reading every sector of every surviving drive. On this build that is about 36 TB of reads. At a realistic 80 to 150 MB/s, with the array still serving files, that is roughly 67 to 125 hours. For the whole of that window there is no redundancy left, and the drives being hammered are the same age as the one that just died and often from the same manufacturing batch.

Applying the manufacturer's unrecoverable read error rating of one per 10^15 bits to that read volume gives roughly a 25 percent chance of meeting one. Read that figure carefully. The rating is a warranty floor rather than a measurement, observed rates across large fleets run substantially better, and modern systems survive a single read error rather than aborting: ZFS reports which file was affected and carries on, and mdadm can be told to continue. Use the number to rank layouts against each other, not as a prediction. The drive failure probability calculator puts annualised failure rates against your own drive count.

The conventional answer is still the right one. Past roughly 8 to 10 TB per drive, run double parity. At 12 TB you are past it. Take SHR-2, take the 24 TB, and revisit when you upgrade the drives.

What can you skip?

The NVMe cache, almost certainly. It is the single most over-bought accessory in this category. A read cache accelerates random access to frequently used blocks. A home media library is sequential, so the cache hit rate is close to nothing and the money does nothing at all. A cache earns its place when you are running virtual machines, databases or a photo catalogue with thousands of thumbnails being generated. Note also that the DS925+ wants Synology-branded drives such as the SNV5420 for storage pools, which is exactly the sort of vendor lock worth knowing about before you commit.

Extra memory, at first. Four gigabytes of ECC is enough for file sharing, Synology Photos and a handful of containers. Memory becomes the limit when you add virtual machines. Buy it when you hit it, not before.

A fifth drive, if you were considering an expansion unit. Expansion chassis are appealing and they add a second point of failure and a cable that must never be knocked. If you need more than four bays, the honest answer is usually the eight-bay build rather than a four-bay with a box hanging off it.

Do not skip the backup or the UPS. RAID protects against a drive dying. It does nothing about accidental deletion, ransomware, a controller writing garbage to every member, theft, fire or flood, because each of those reaches all four drives at once. And an unclean shutdown during a write is one of the few events that damages an array rather than a drive. Between them, the external drive and the sine wave UPS cover the failures parity cannot.

What should you upgrade first?

• An offsite third copy. A second 20 TB external kept somewhere other than your house, rotated quarterly, is the highest-value $700 you can add. Fire and theft reach every device in one building, and no amount of parity helps.
• Memory, when containers start swapping. Cheap, and the effect is immediate.
• Capacity, at 80 percent full. Under SHR that means two larger drives rather than four, which is the entire reason this build is a Synology. Plan the sequence with how to migrate to a bigger NAS, and note that a drive-by-drive upgrade means running one full rebuild per drive.
• Not 10 gigabit. Four spinning drives cannot saturate it. See 2.5GbE against 10GbE for the arithmetic.

What does it cost to leave running?

Four drives at 6 to 9 W idle plus an x86 board at 15 to 20 W puts this build around 45 to 56 W idle, rising to roughly 70 W under sustained load. At 8,760 hours and 17 cents per kWh, using W / 1000 x 8760 x tariff, that is about $67 to $83 a year, or $335 to $415 over five years. That is roughly half the price of the enclosure, spent quietly. The power draw calculator takes your own tariff, and the power consumption chart has the per-component figures.

Where this build sits against the others

Most people who read all three of these pages should build this one. The beginner tier fills faster than buyers expect once video enters the picture, and the expert tier is a $7,890 commitment whose main benefit, four times the usable capacity, is only worth paying for if you can name the data that will fill it.

Related reading

• Cross-vendor RAID capacity calculator, including mixed drive sizes
• Best NAS for home, the enclosure alternatives
• Best NAS hard drives, where half this budget goes
• SHR against RAID 5, the reason this build is a Synology
• Synology DS925+ full specifications
• All three complete builds compared