Building a small always-on box for file storage and a handful of containers. I want to stay near 40W at idle because it runs 24/7 and electricity here is expensive. Both options give me 8TB usable and cost about the same secondhand. The four drive option is faster on paper. I have no plans to expand beyond this case, which fits four drives. What actually matters for a home setup at this size?
Two drives mirrored, for power and for rebuilds. Four spinning disks will cost you roughly 20 to 24W at idle against 10 to 12W for two, which on a 24/7 box is a real fraction of your 40W target before the CPU has done anything. Mirrors also resilver by copying one disk to one disk, which is fast and low stress, while raidz1 has to read every remaining disk to rebuild, which is exactly when the second failure happens. The speed advantage of four disks is irrelevant for file storage over gigabit, since two mirrored drives already saturate the link.
The rebuild argument is more persuasive to me than the power one, honestly. Does the mirror leave me any expansion path at all?
Yes, and a good one: add a second mirrored pair later into the same pool, or replace both drives with larger ones one at a time. With four disks in raidz1 and a four bay case you are finished forever.
Measure before you optimise. A cheap plug-in power meter will tell you what the box actually draws, and in most builds I have measured the platform, the power supply efficiency at low load, and the drives spinning up rather than idling matter more than the drive count. An oversized 750W supply running at 8 percent load can waste more than two extra disks.
Seconded. Going from a large old supply to a modest efficient one saved me 15W at idle, which was more than any disk decision.
Neither layout is a backup. Whichever you choose, budget for a copy that is not in that box, because the most likely thing to kill both drives at once is a power event or a mistake you make yourself.
@chmod_confused · 10mo ago
Four smaller drives secondhand also means four sets of unknown hours. Two drives means half the chances of drawing a bad one, which at this scale is not nothing.
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