A TrueNAS Build That Makes Sense: Choosing the Chassis
Purpose-built NAS boxes charge a premium for the word NAS. A refurbished 2U server with a proper drive backplane, an HBA and ECC memory runs TrueNAS better than most appliances — more bays, more RAM ceiling, real out-of-band management — and usually costs less. The build decisions that matter are the chassis bay layout, the controller, and memory. Everything else is detail.
Bay layout decides the pool you can build
For bulk capacity on spinning drives, 12× 3.5" (12LFF) is the classic layout: a Dell R730xd 12LFF or an HPE DL380 Gen9/Gen10 12LFF swallows twelve NAS or enterprise SATA/SAS drives. Twelve bays map neatly onto two six-wide RAIDZ2 vdevs — a balanced design that survives two failures per vdev and rebuilds at tolerable speed. With 12–16TB drives that is 120–160TB usable from one box.
For an all-flash pool or a mixed design, 24SFF gives flexibility: mirrors for fast datasets, small SAS drives for archives, easy incremental growth by adding pairs. Flash pools also sidestep the long-rebuild anxiety that pushes people toward RAIDZ2 on big spinners.
The R730xd has a further trick: rear 2.5" flex bays, ideal for a mirrored boot pair or L2ARC/SLOG devices without spending front bays.
The controller rule is absolute
ZFS must see raw disks. That means an HBA (an LSI/Broadcom SAS card in IT mode) or a RAID controller with a true passthrough mode — Dell HBA330 is the clean answer, H730 in HBA mode is acceptable; on HPE, the P440ar in HBA mode works and the software B140i should be avoided. Hardware-RAID virtual disks under ZFS hide device errors from the filesystem that exists to catch them.
Memory: generous, ECC, and boring
The old 1GB-per-TB guidance is a starting point, not a law — but ZFS uses RAM as its read cache (ARC), so capacity translates directly into hit rate. 64GB is a sensible floor for a 12-drive pool; 128GB is comfortable; more helps if many users hit the same working set. Every refurbished platform in this class takes cheap DDR4 RDIMMs, so this is the least expensive upgrade on the sheet.
What about SLOG and L2ARC?
Only add a SLOG device if you have synchronous writes — NFS for VMware, databases, iSCSI with sync enabled. Then use a power-loss-protected enterprise SSD; a consumer drive is worse than none. L2ARC earns its keep only after RAM is maxed and the working set still exceeds ARC. Most home and small-office builds need neither on day one.
Two reference builds
Capacity: R730xd 12LFF, 2× E5-2620 v4 (storage barely uses CPU), 128GB RDIMM, HBA330, twelve 10TB SAS drives as 2× RAIDZ2, rear mirrored SSDs for boot. Performance: DL380 Gen10 24SFF, 2× Silver 4110, 128GB, HBA-mode controller, twelve 1.92TB SSDs in mirrors with room to grow, dual 10GbE SFP+.
Both are quiet enough for a back office, ship with redundant power, and leave the door open to add a disk shelf later — which is a whole article of its own.