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. > 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.) > Sometimes, using the M.2 slots on the motherboard will disable > certain SATA ports. I'm aware. I've read motherboard reviews in some depth, and planned my motherboard selection and drive purchases in part around the motherboard SATA-port capacity after taking such disabling into account. > Most of the time, I try to reduce the number of drives to a sensible > minimum (four seems to be pretty standard for client systems) and > rather chose larger disks but fewer. YMMV. It's reasonable, and in an ideal world I'd prefer to do that myself; prior to starting to work out the numbers, I was expecting to go for a 4-to-6 drive max on the SATA side of things. However, once I actually did the calculations, my constraints are what they are. >> card, a collection of fans, and of course whatever the motherboard >> and case may need (not excluding USB ports and the devices attached >> to them). > > 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. > and only afterwards think about storage. I could estimate 30W for > 2x15W SSD + 20W for 2x10W HDD. This would total at 435W i.e. 550W PSU > would suffice. Of course, if the GPU were to be upgraded or > significant amount of RAM were to be added, that would have to be > added as extra. Most of the time, I am relying on > manufacturer-provided PSUs and for my T5820 configuration, Dell's > smallest choice was 950W (more than enough...) > > The heavier the GPU, the more sense it makes to chose much larger a > PSU than by the estimate, because modern GPUs tend to require > "spikes" of power in very short time that can destroy PSUs that would > otherwise suffice. I have not found a means to find out about this in > advance other than reading exstensive reviews for the respective GPUs > of interest. All reasonable; thank you. By that metric, I'd probably be targeting something in the range from a 650W-800W PSU; that's a step down in capacity (and therefore probably up in efficiency, as well as in price) from my current machine's 1KW unit. I will of course apply at least one online power-supply calculator just to see if I can get any meaningful benefit out of it, but I don't expect it'll change the results much. -- The Wanderer The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man. -- George Bernard Shaw
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