UNAS Pro 4 vs UNAS Pro 8: Same Processor, Twice the Bays

These two share a processor, a cache design and a pair of SFP+ ports, which makes this a clean matchup. Against the seven-bay UNAS Pro the Pro 8 changes nearly everything. Against the Pro 4 it changes a short list, and the list is easy to price.

In fact, the larger unit is the cheaper one per bay. The Pro 4 works out to $125 a bay and the Pro 8 to $100, so the 60% premium buys 100% more room. However, a bay is only worth paying for once there is a drive to put in it, and Ubiquiti sells the drives separately.

Both are among the three rack-mount models this site tracks, and the Network Storage hub sets all three side by side. Additionally, UNAS Pro vs UNAS Pro 8 covers the seven-bay unit that shares the Pro 4's price.

This section decides more purchases than the price does, because the intuition runs the wrong way. After all, a unit that costs 60% more reads as the faster machine. On the processor and the cache, it is the same machine with more room in it.

Of course, memory is the exception, and it is a real one. The Pro 8 lists 16 GB against 8 GB. Ubiquiti publishes no throughput figure for either model, so this page will not say what the extra memory is worth in megabytes a second. It is reasonable to expect a busier share to benefit, and unreasonable to put a number on it.

Most of the software list does not move either. Both sheets show SMB and NFS, RAID 5, 6 and 10, snapshots, file encryption, Time Machine backup, and backup to a remote UNAS, an SMB server or a cloud service. Accordingly, the two rows that do differ, RAID groups and hot spares, get the next section to themselves.

Note that the missing row is a fact about the spec sheet. Ubiquiti prints "Hot Spare Support" for the Pro 8 and for the seven-bay UNAS Pro, and prints nothing for the Pro 4. This page will not read that as "unsupported", because the sheet does not say so. A build that depends on a hot spare should confirm it with Ubiquiti first.

The arithmetic of four bays matters more than either row. Standard RAID 6 spends two drives on parity, and RAID 10 mirrors half the set. As a result, a four-bay array in either level keeps two drives' worth of capacity, which is half of what was bought. RAID 5 keeps three, with one drive of protection.

Eight bays change those fractions. For instance, RAID 6 across eight drives keeps six, so the parity cost falls from a half to a quarter. That is the strongest capacity argument for the Pro 8, and it holds at any drive size.

On the Pro 4, anything faster than gigabit has to arrive over SFP+, and at 10G. That suits a rack with a 10G switch in it. The USW Pro 24 PoE and USW Pro Max 24 PoE each carry two 10G SFP+ ports. Keep in mind that those two ports are usually the switch's uplinks as well.

The Pro 8's copper port removes that constraint. It links at 2.5G or 5G to multi-gig switches and clients, and at 10G to a port such as the RJ45 uplink on the USW Flex 2.5G 8 PoE. What's more, it leaves both SFP+ ports free.

Neither sheet says how the two SFP+ ports may be combined, so this page does not either. Be aware that a bonded pair would not double a single file copy in any case. Switch uplinks and link aggregation sets out why, and it names NAS hosts as one of the cases where a bond does earn its ports.

However, power is where the two designs part company. The Pro 4 lists one internal 150 W supply and a USP-RPS DC input. The Pro 8 lists two hot-swappable 550 W modules on two AC inputs. As a result, both sheets say yes to power redundancy, and only one of them says it without a second purchase.

That purchase is easy to price. Ubiquiti lists the USP-RPS at $399, which makes a Pro 4 with redundant power a $898 build. That is $99 more than a Pro 8, which has twice the bays. Naturally, a rack that already holds a USP-RPS with a free output changes the sum, and the $300 gap returns.

The drive budgets rise with the bay counts, to 125 W for the Pro 4 and 225 W for the Pro 8. Ubiquiti does not say how either figure divides between the bays and the two M.2 slots. Treat each as a ceiling to check a planned drive set against.

Buy the UNAS Pro 4 when the data fits and the rack is tight. These are the cases it wins outright:

• Four bays are enough for years, not months. Size the array after parity, not before it, and leave room to grow.
• The rack is short on height or depth. 1U and 400 mm go where 2U and 480 mm will not.
• There is a 10G SFP+ switch port free, and a USP-RPS already in the rack. Both of the Pro 4's compromises then cost nothing.

Buy the UNAS Pro 8 for the opposite cases. For instance, it is the right unit when RAID 6 on four bays gives away too much, or when clients connect over multi-gig copper. It is also the right unit when redundant power is required and no RPS is installed. Overall, it is the same processor and cache with fewer corners cut around them, and the per-bay price is lower.

That said, if capacity is the whole brief and cache is not, the seven-bay UNAS Pro costs the same $499 as the Pro 4. Camera recording belongs to a different appliance, and NVR G2 vs NVR G2 Pro is the place to start.