For my smaller (16 HDDs at present in four arrays) I really like the open 4 bay arrays. My favorite is no longer available, but this one still is:
It is 5Gb/s USB 3.0 and you can easily use over ten of them with powered USB 3.0 5GB/s splitters and not need the PSU for the HDDs.
Was trying to stay away from USB and keep them connected directly to the MOBO somehow. Iāve seen people having a lot of problems with lots of USB connections. I was planning to try to add around 30 drives in this manner.
I would assume that that card also staggers those starts. Again, once dust settles, those drives will take ~8W each, what is well below even 100W. That leaves plenty of room for those drives that may be potentially struggling to finish their start.
It may be that your PSU is old/bad. However, I would rather do fsck first on that drive, as my take is that this is just some format / clusters problem, not really power related. Although, maybe you have some bad molex there.
I have the 2-bay version of that somewhere around here and love it - great for quickly getting a naked 3.5" drive connected!
OH well in that case you probably will like my old thread if you havenāt seen it yet: Scalable DIY SATA JBOD - Will store over 250 Disks! - Chia Farming & Harvesting - Chia Forum
This was before I moved over to the Dell SC200ās. Lots of info there about using power supplies and GPU breakout boards and all kinds of fun stuff.
I donāt know if theyāre getting staggered though. My PSU that I use to power the drives isnāt connected to a motherboard. Itās shorted to allow power all the time. When I plug the PSU in, I think all of the drives start at one time. Usually, with my setup, I plug in the PSU that powers the drives, and let the drives start, then I turn my server on. I just assumed this was the order that this setup needed to be started up from a shutdown. The drives need to be on when the server starts.
Staggering is controlled via data link, not via power. Drive will get 5/12V, but the data part will hold it back. However, if your card is not powered, maybe those drives start all at the same time. Still, having 400W for 9 drives (as you have right now), is way below what that PSU could do.
Peeps having USB problems have bad setups somewhere. Many swear by their USB 2.0 but still complain of long response times.
All of my HDD arrays are on USB 3.0 SS 5GB/s ports and use USB 3.0 5Gb/s powered hubs.
With this setup my avg response time is around .12 seconds with longest responses under 1.7 seconds. Even when writing plots I do see response times drop but never miss challenges.
My efficiency runs at about 102% and I credit this to my fast response times. 
That may not be the true. Most controllers allow for hot-swap, as such drives may come late. Potentially, connecting them late would let the card to still do some staggering (if they would be not fully spinning). Again, I donāt think that this is your issue right now.
Ah. These definitely do allow for hot swap! I didnāt even think of that. Next time I shut down for something, I will try changing my order and start the drives up after the OS has booted up. Thanks for bringing that to my attention!
If you have dedicated the PSU than it can power many HDDs, probably even your 20.
I would be more concerned about too many power splitters as I got towards 20 drives.
Again, I doubt that this is your problem.
If you are still concerned about PSU, just unplug one of the good drives, and see whether the one in question will start working. Apparently, if that would be a PSU border line, it will be crossed by the ālastā drive.
I know I doubt itās the problem, but I want to see if starting up that way will spin the drives up individually.
There is no magic in āstartup.ā When you start your box, it doesnāt imply that your drives are getting power right away (yes, most likely they do, but donāt have to). If you watch your boot screen, you will see that your SAS/SATA card is scanning for drives for some time. So, you can think about starting your box first, and your drives second as kind of lazy startup of the whole thing. If you wait for longer, that will be more like a hot-swap start.
I do have a dedicated PSU. It came with 4 SATA power connectors and 4 molex connectors. I bought 3 molex to 4x SATA power. My plan was to use the 4 sata power connectors and one molex to power 8 drives, then use the remaining 2 molex connectors to power the other 8 drives.
I think yer good. Let us know the results! 
If you do try for 20 in future, individually splitting each of the 4 SATA power connectors once would not cause any local load issues, and dedicated, your 400W PSU should not have total load issues either even when accounting for any spike surges.
Ok. Idk if you saw in the picture, but I have the PSU plugged into a BBU. Should be conditioning the power to it. Iāll let you know how it works. If I continue having troubles, Iāll probably just buy an old server PSU, and a breakout board for HDD mining. I think they make them now with 5vā¦ Iām not 100% on that thoughā¦
My understanding is that one drive may draw over 20W of power when starting up (per Seagate X16 data sheet). I donāt recall what is the split of those 5V (board and heads stepper ?) and 12V (spindle), but 5V also spikes up during startup. So, for a ānormalā PSU, you may want to check your 5V limits.