Common questions on NAS, RAID and drives

Because the maker and the operating system count differently. A drive maker calls one trillion bytes a terabyte. Your NAS counts in powers of two and calls 2 to the 40th bytes a TiB. The gap is about 9 percent: an 8 TB drive shows up as 7.28 TiB. Nothing is missing, it is just counted differently — which is why our calculators always show both numbers.

No, and it is the most expensive misunderstanding in storage. RAID protects against one drive failing and nothing else. Accidental deletion, ransomware, a lightning strike, theft or a filesystem error all hit every drive in the enclosure at once. You still need a real backup in a second location.

With equal-size drives, none: both give the same usable capacity and both survive one drive failing. The difference appears with mixed sizes. RAID 5 sizes to the smallest drive and leaves the surplus on larger drives unused; SHR subtracts only the largest drive and uses the rest. Synology has SHR, TerraMaster does the same with TRAID, UGREEN and QNAP do not.

Once you run a RAID array, yes. SMR drives write their tracks overlapping and have to reorganize whole regions on overwrite. During a rebuild after a failure, their write rate collapses so badly the process can take days instead of hours. Every Seagate IronWolf series, plus WD Red Plus and WD Red Pro, are CMR.

Yes. In April 2025 Synology announced that the 2025 Plus models would only create a storage pool with listed drives. DSM 7.3, on 8 October 2025, reversed that lock for hard drives and 2.5-inch SATA SSDs. Only M.2 NVMe still requires a listed drive. Older models such as the DS923+ were never affected.

For a turnkey NAS that stores files and pulls backups, the factory memory is almost always enough. The question gets interesting with TrueNAS and ZFS, where the old rule '8 GB plus 1 GB per TB' circulates. It dates from the FreeNAS era and over-provisions badly at scale: at 120 TB it asks for 128 GB, while 64 GB is comfortable in practice.

Only if you read the same data repeatedly — project files, photos, containers. Streaming a media library through once gains nothing, because that data is read exactly once. Check your network too: on a gigabit link you top out around 110 MB/s, which a single drive already reaches.

The drives dominate the bill, not the processor. A 3.5-inch NAS drive draws about 4 to 6 watts idle, so a four-drive NAS lands around 40 watts — roughly 350 kWh a year. What that costs depends heavily on your province: at Quebec's low residential rates it is only a few dollars a month, while Ontario or Alberta rates cost noticeably more. We work power figures against real provincial rates rather than one national number.