Planning circuit for HDD array question 8x
Planning circuit for HDD array question 8x
I'm working on constructing this disk array enclosure to connect to my NAS. I've created the v0 circuit diagram using the photos and description from the original designer. However, I'm worried about whether it can meet the power needs of the enterprise HDDs I purchased (source, spec). All the information I found online and in the HDD specifications suggests that the 12v rail should be capable of handling 2 amps peak. For all 8 drives spinning up together, that totals 16 amps. I'm aware enough to be risky.
I consulted with friends and came up with these designs.
* One suggested looping the power connections as shown in diagram v4
* Another expressed concern about creating a ground loop, which was resolved by removing loops in v5
Notes:
* The 5v rail only requires 3.5 amps
* According to the specs I've read, the Minifit & Microfit Jr connectors used for PCIe and my power supply should manage at least 6 amps per conductor with 18-gauge wires. This would allow 18 amps for 3 x 12v and 3 x common. BUT, I just discovered the PCIe connector spec only permits
6.25 or 12.5 amps.
Thus, I might need to modify my circuit to accommodate more power from PCIe.
* I haven't considered peak versus normal load. I'm uncertain about how to define peak usage frequency and duration. Therefore, it seems safer to design for peak as if it were constant.
Your advice would be appreciated.
Diagrams
Commercial NAS systems start up in a staggered manner. Two drives are initialized first, then wait briefly before proceeding to the next two, and so on.
True. My HBA allows staggered spin-up, but after initialization the OS handles standby and spin-up. Unfortunately, UNRAID only offers staggered spin-up during boot, not when drives are in standby mode.
16 amps (12v 192 watts) is a reasonable power supply for today. The main concern is safely delivering it to the drives. My considerations are:
* Connecting from the main power source, which is currently idle, as I plan.
* Using a FlexATX PSU inside the drive case. These usually support only a few drives, so I’ll need to create custom wiring.
* Ensuring proper order of turning on and off the connections.
* Whether I should link the grounds from both PSUs?
EDIT: Third choice—start staggered but avoid standby mode.
DIY presents difficulties but can be enjoyable.
They often claim that most engine wear comes from cold starts. Once it's running, fluid dynamic bearings avoid metal-on-metal contact and thus experience no wear. Over time, they remain effective until seals break down and oil escapes. The only drawback is higher power usage during idle. Nowadays, manufacturers have adopted stop-start systems to boost fuel efficiency by about 2%, but they seem more focused on warranty periods than long-term performance.
Deciding whether to spin-down the drives is likely the most discussed issue in the UNRAID community. Given the current size of my array, it probably isn't worthwhile to save money by spinning them down each year. The potential savings increase as I grow the array and electricity costs rise (for example, saving $80 per year when I reach the projected rate hikes).
In reality, my array is primarily for archival purposes—backups and camera recordings with no live writes. With directory caching, scheduled writes, and UNRAID's file allocation strategy, only a few drives are expected to be active daily. I could set the standby timer to 24 hours to reduce unnecessary spinning, allowing half of the drives to remain idle for weeks at a time.
I still haven’t reached a clear conclusion on either side of this debate.
Looking for affordable electricity options in my area. I calculated that running one of my 8-disk TrueNAS Core servers around the clock for a year, using 120W, would use about 1051.2 kWhr. At $0.32 per unit, that comes to roughly $336 a year. I don’t run them nonstop.
I’ve noticed no issues when starting 8 or 10 Enterprise disks at once, as long as I use a good quality PSU. I can’t view your Imgur link right now, so I can’t confirm the wiring diagrams you provided.
My builds mix SAS and SATA drives, but I haven’t added power-on delays for pairs of disks. In data centres, professional systems were used, but at home I’m more relaxed—just keeping backups.
Peak current on a hard disk’s 12V rail spikes when the motor starts up. The platters reach speed quickly and then the draw drops. Manufacturers list peak and normal currents in their specs—check yours.
Cables handle short overloads, and connectors too. Going too far can cause damage, but using high-quality PSU cables with multiple SATA connectors works well when needed.
Don’t overcomplicate hard disk power connections. Excessive complexity is just wasted time and effort.
The main difficulty lies in transmitting power securely from the internal PSU to the external enclosure. Managing the total amperage from eight drives across one cable and connectors was the main issue. My current schematic covers only half of the drives, allowing for a more manageable current load. I can easily replicate the circuit to incorporate the remaining half (excluding the fan and LEDs).