The Wanderer writes:
On 2021-03-07 at 21:35, Linux-Fan wrote:> Btw. wrt. the thread's main topic: I saw many disks being discussed. That was in a separate message, so a separate reply would have been appropriate (to preserve threading by sub-topic), but yes.
Yes, sorry for that. I initially started replying to just the first thing and then remembered that I might comment on the other things, too...
> The Wanderer wrote: > >> Any power-related advice for SSDs? > > It highly depends on the models. The ones I am using are rated 14W by > the manufacturer (operating/loaded). I expect other SSDs to use less > power although it might make a good rule of thumb to just assume "15W > per drive" for safety? > >> In the system I'm planning to build, I'm expecting to have >> something along the lines of two M.2 SSDs (RAID-1), presumably in >> the NVMe 2280 form factor you specify, and eight or more SATA SSDs >> in a 2.5" form factor (RAID-6), along with a discrete GPU, probably >> a discrete sound > > Is there a specific reason for having so many drives? A combination of three reasons: the desire for RAID (to be resilient against drive failures), the need for a certain minimum total capacity (to avoid capacity loss relative to the existing system which this is to be built to replace), and the hope to avoid letting the budget balloon past what even I can consider reasonable. The RAID-6 goal means I need a bare minimum of four drives on the SATA side of things. To achieve the capacity goal with 2TB per drive and RAID-6, I need (if I recall my calculations correctly) eight total such drives. More than 2TB per drive, with SSDs, gets too expensive for my expectable budget. The reason for counting the M.2 SSDs separately is because of A: their different performance characteristics, B: their different price per gigabyte, and C: that (last I checked) GRUB wouldn't support booting from mdadm RAID-6 but would from mdadm RAID-1, so I need a separate RAID-1 in any case, and connecting those drives to physically different ports makes a good way to split it out. (The RAID-1 will get the "system" partitions, and the RAID-6 the "data" partitions - the latter being largely /home and /opt, since I've learned that /var should really be counted in the "system" category.)
Makes sense, yes. I'd be interested to hear how it performs once it is online :) No first-hand experience with RAID6 here...
[...]
> Wrt. power I usually start from CPU + GPU (e.g. for my system that > would be 165W CPU + 150W GPU, then add some estimate for > motherboard+fans (e.g. 70W -- derived from the previous' system's > idle power usage) How did you measure / calculate that latter? I have mine plugged in through a wall box with a display, but am not sure the result is reliable, given the multiple components and the variability of power draw - and of course having such a thing in the power chain is not typical for most people.
My measurement is at least as unreliable as yours. I turned off the other components and then read what the UPS' power meter says. Given that at the same time, an ethernet switch and small (ARM SBC) computer were still attached and online, I expect my 70W to include some of their power draw, too. My previous machine was an 1U server (named pte5) and there, `sensors` also reported a (probably even less reliable?) measure for the PSU power draw which was at around 50-65W for typical idle states IIRC.
Before I had the server, I used a HP Z400 workstation (masysma-3) for which I had measured (using a cheap power meter attached to the wall outlet) about 80W idle power draw. For the current system (masysma-18) again measured including ethernet switch and an idle Intel NUC (larger small computer :) ), the UPS reports around 100W.
To summarize, here are my "idle" power measures:
System PSU Size Measurement Reported by Components included
masysma-3 475W 80W cheap meter just the computer
pte5 300W 70W UPS computer + switch + ARM SBC
50-65W sensors/PSU just the computer
masysma-18 950W 100W UPS computer + switch + Intel NUC
Of course, all of these systems have differently sized RAM, CPUs and GPUs.
Only the number of HDDs is pretty constant with four for each machine (it
was 2x3.5" HDD + 2x2.5" SSD at the time of measurement).
Note that the UPS' power meter is probably even less reliable than the wall- plugged dedicated devices for the purpose. When I shutdown the main system, it constantly reports 0W although switch and Intel NUC are up and running :)
[...] HTH Linux-Fan ΓΆΓΆ
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