Scenario 4 — backup growth on stocked hardware
Date: August 2026 · Status: not retained as a scenario —
scenario 3 was retained on 2026-08-20. This page stays as
the priced LFF growth step behind pbs-01, to be taken if the store outgrows its bays.
Scope: Scenario 3, unchanged in compute, network, homes, sites,
services and order of operations — everything not on this page is inherited from there by
reference. The one delta is in the backup section (scenario 3 §5):
the LFF growth step, which scenario 3 could only price as an empty MD1200/MD1400 listing, is made
concrete with hardware in stock today — an HPE D3600 12 × LFF SAS shelf behind pbs-01.
Block diagram
Only the backup leg is drawn — the rest of the topology is scenario 3's, unchanged.
1. What changes against Scenario 3
| Scenario 3 section | Here |
|---|---|
| §1 role map, §2 decisions, §3 compute, §4 homes | inherited unchanged |
| §5 backup | the two R740xd all-NVMe boxes stay as-is; the LFF growth step is respecified on the D3600 — §2 and §3 below |
| §6 network, §8 services, §11 order of operations | inherited unchanged — the shelf is a growth step, not a phase |
| §7 sites, power, racks | inherited, with one delta to carry: a shelf is 2 U and ≈ 200 W per site — §4 |
| §9 buy list, §10 open items | growth lines added — §5 and §6 below |
2. Backup — the growth table revised
The chain itself does not move: pbs-01 (307, nightly vzdump of every guest plus the homes from
filer-01) is the Dell R740xd 24 × SFF all-NVMe box of scenario 3, 8 × PM983 RAIDZ2 ≈ 10.5 TiB,
and the sizing argument (171 GiB measured store, 2026-08-14) is unchanged. What changes is
the last row of the growth table: scenario 3 records that no Dell LFF shelf is listed and points
here for the step itself, which this page specifies on hardware the vendor stocks today.
Growth, in the order it should be taken:
| Step | What it costs |
|---|---|
| 4 more PM983 (a second RAIDZ2 vdev) | free — from the spares |
| Fill the remaining bays with SATA SSDs | market price, any 2.5" drive fits |
| A Dell SC220 shelf, 24 × 2.5", 6G SAS | €42 net, 13 in stock, plus an external SAS HBA — still the cheaper intermediate step |
| An HPE D3600 shelf with 14 TB spinners — §3 | ≈ €4 000, all lines in stock |
3. The shelf — HPE D3600
The HPE D3600 12G SAS Disk Enclosure (QW968A, servershop24 article a-121875, €672.26 net, used, 2 in stock) is a 12 × 3.5" LFF SAS JBOD: dual I/O modules with 2 × SFF-8644 each, redundant PSUs and fans. Despite the HPE label it is a plain, vendor-agnostic expander shelf — any IT-mode HBA drives it, and the drives appear to the host as raw SAS disks, which is what ZFS wants.
| Piece | What | Cost |
|---|---|---|
| Shelf | HPE D3600, QW968A — 12 × LFF, dual I/O modules, redundant PSUs/fans | €672.26 net, used, 2 in stock |
| HBA | one external SAS HBA in IT mode in pbs-01 — LSI/Broadcom 9300-8e or 9400-8e. Never an HPE Smart Array: ZFS needs the raw disks, not a RAID controller's view of them | ~€60–120 used |
| Cables | mini-SAS HD SFF-8644 ↔ SFF-8644 | from stock, or a few euros |
| Trays | HPE Smart Carrier LFF, 651314-001, one per drive | €16.80, >1000 in stock |
| Drives | 14 TB SAS nearline | €252/unit at servershop24 |
Pool on the shelf: 10 × 14 TB in RAIDZ2 + 2 hot spares ≈ 100 TiB usable, as a separate ZFS pool and a separate PBS datastore with its own, longer retention. The all-flash pool keeps the 14 d / 8 w / 6 m chain; the shelf holds what should outlive it. Two rules:
- Single-path cabling for the first pass — one SFF-8644 run into one I/O module. Cabling both
modules gives path redundancy but puts
multipathdbetween the disks and ZFS; that is an option to take deliberately later, not a default. - SATA drives are excluded. The bays accept them physically, but a single-port SATA drive behind the SAS expander loses the dual-port topology the shelf is built around — SAS nearline only.
4. Caveats
- Nothing is ordered now. The measured store is 171 GiB; this page specifies the growth step so it can be taken from stock when the semester review (scenario 3 §10) says so, not sooner.
- Only 2 D3600 are in stock today, and one is needed — scenario 3 has a single PBS box. The listing can empty at any time, so whether to take the second unit as a shelf spare is decided at order time.
- The SC220 stays in the table before the D3600. At €42 for 24 × 2.5" bays it remains the cheaper intermediate step; the D3600 is the step after, when retention needs LFF economics (18 €/TB on the 14 TB drives against 105 €/TB for 2.5" SAS).
- A shelf is 2 U and ≈ 200 W, which §7 does not account for. Space is the easy half — 307 keeps 9 U free. Power is the tighter one: the shelf lands on the existing 2 kVA UPS already carrying ≈ 0.9 kW continuous. Measure before ordering.
5. Buy list — delta
Additions to scenario 3 §9; same source and terms (ServerShop24, 14 August 2026, net, excl. VAT and shipping — stock moves, confirm against a live quote). Every line here is growth, not ordered — none of it joins the phase-0 order.
| Item | Qty | Unit | ≈ total | For |
|---|---|---|---|---|
| HPE D3600 12G SAS Disk Enclosure (QW968A) — used, 2 in stock | 1 | €672.26 | €672 | LFF shelf behind pbs-01 — growth, not ordered |
| LSI/Broadcom 9300-8e or 9400-8e, IT mode, used | 1 | €60–120 | €60–120 | external HBA in pbs-01 — growth, not ordered |
| HPE Smart Carrier LFF tray, 651314-001 (>1000 in stock) | 12 | €16.80 | €202 | one per drive — growth, not ordered |
| mini-SAS HD SFF-8644 ↔ SFF-8644 | 1 | ~€10 | €0–10 | from stock if it holds any — growth, not ordered |
| 14 TB SAS nearline | 12 | €252 | €3 024 | 10 × RAIDZ2 + 2 spares — growth, not ordered |
| Subtotal, growth | ≈ €4 000 |
6. Open items — delta
Additions to scenario 3 §10:
| Item | Blocks |
|---|---|
| D3600 stock — 2 used units listed, one needed. Take the second as a shelf spare while stock lasts? | the order quantity |
An R740xd 24 × SFF all-NVMe spends PCIe lanes and slots on backplane extender cards — is a slot left for the external HBA, next to pbs-01's 10 G NIC? | whether the shelf can hang off the PBS box at all |
| The 2 U and ≈ 200 W of the shelf against §7's 307 load line | the UPS margin, and whether a shelf in 307 needs the UPS resized |
| Does the cable stock hold mini-SAS HD SFF-8644 ↔ SFF-8644? | a few euros otherwise |
| 9300-8e/9400-8e — confirm IT-mode firmware on the used card, flash if not | the shelf's ZFS pool |
| Semester store-size review (already in scenario 3) — the trigger for the SC220 step, then this shelf | when any of this is bought |