Buying

Drives: class, not SKU

The enclosure is half the purchase. The disks are the other half — and the part we refuse to fake a compatibility list for.

What this planner assumes

NAS-rated CMR drives. Desktop disks, archive SMR disks, and USB enclosures are a poor fit for a 24/7 bay. That is an editorial rule (R), not a lab ranking of every SKU on sale this week.

How many, of what size

• 2-bay mirror — two drives of equal capacity. Usable space is roughly one drive.
• 4-bay single-parity — four drives of equal capacity. Usable space is roughly three drives.

The planner rounds a size band up from the planning target. Exact usable capacity still depends on RAID/SHR, filesystem and the specific drive. We do not apply a hidden overhead multiplier.

Common capacity bands

These are merchant searches for sizes people actually buy, not a recommendation for your household. Run the planner for a band that follows from your numbers.

What waits for a later layer

A live HCL, firmware notes, and “this exact WD / Seagate / Toshiba model is listed for this exact enclosure” is Layer 4. Shipping it as a guess would be the kind of confidence this site is built not to have.