scottw Posted October 6, 2008 Share Posted October 6, 2008 I just bought a 500w PSU and want to be able to measure how much is being used of it so I know how many drives I can add. I know there are calculators and I know my PSU can probably handle around 9-12 drives but would like to know for sure so I don't over-do it. Thanks, Link to comment
scottw Posted October 6, 2008 Author Share Posted October 6, 2008 SORRY,SORRY,SORRY,SORRY....I just found a post on this. I assume the Kill-A-Watt meter is what I need right?? Don't harm the NEWBIE Link to comment
RobJ Posted October 6, 2008 Share Posted October 6, 2008 The Kill-A-Watt is a great tool for measuring watts usage by different components. I have one, and numerous other users do too. However, it is too slow to measure the startup peaks, as are most electrical testers. They provide measurements of current usage, but not usually peak usage. And that is what is more important for sizing a power supply. Startup needs are much higher than operational usage, even under the heaviest loads. I'm afraid the best advice is the manufacturer's specs AND reports from other users, as well as comparative reviews and advice. Link to comment
scottw Posted October 6, 2008 Author Share Posted October 6, 2008 Ok thanks....so I guest the safest "test" would be if drives have trouble spinning up then I have a problem, right Link to comment
WeeboTech Posted October 6, 2008 Share Posted October 6, 2008 However, it is too slow to measure the startup peaks, as are most electrical testers. It's good enough to an idea. You just have to constantly watch it during every step of the way. I would see one of my dual xeon servers peak at 300w, then settle down to 160w after the kernel was loaded and idle. Link to comment
WeeboTech Posted October 6, 2008 Share Posted October 6, 2008 Yes scottw... also, how many drives do you have in there now? What models? Are they recent or the WD green drives? Link to comment
scottw Posted October 6, 2008 Author Share Posted October 6, 2008 Yes scottw... also, how many drives do you have in there now? What models? Are they recent or the WD green drives? Just 3 250 7200rpm drives right now...just bought the PRO license today You have the same PSU as me (Seasonic modular) and have 9 drives on it, that's where I got that number from. I just wanted to know what to expect if I overload it and if I can prevent that. Thanks, Link to comment
RobJ Posted October 6, 2008 Share Posted October 6, 2008 Ok thanks....so I guest the safest "test" would be if drives have trouble spinning up then I have a problem, right That is probably right, but it is not as simple as that. Many PSU's have multiple rails (supposedly electrically independent supplies), and if there are too many components on any one rail, then one or more components might not be able to power up, even though the overall specs look adequate. A quality one rail PSU won't have that problem. Also higher temps can affect the available power, but this is not usually a major startup issue. It's good enough to an idea. You just have to constantly watch it You are right, for a rough idea. I'd want to reboot 4 or more times, and watch for the very highest value, since it is polling, and you are hoping for a sampling as close to a peak as possible. I'd like to hear an expert opinion on how much higher the true max power draw usually is, over the highest polled value. Link to comment
yodine Posted October 6, 2008 Share Posted October 6, 2008 I have 12 drives and a core 2 duo 3GHz and the max Watt it took was 325W, of course at startup. But all drives awake, it will eat less than 200W and will go down 79W when all the drive spindown. Link to comment
WeeboTech Posted October 6, 2008 Share Posted October 6, 2008 I just wanted to know what to expect if I overload it and if I can prevent that. Drives may fail to spin up or the system will lock up at random points. A common place is during a massive spin up by unRAID, the button, a SYNC call or a shutdown (Whch does a sync). Intermittant drives falling off the bus. Link to comment
WeeboTech Posted October 6, 2008 Share Posted October 6, 2008 I have 12 drives and a core 2 duo 3GHz and the max Watt it took was 325W, of course at startup. But all drives awake, it will eat less than 200W and will go down 79W when all the drive spindown. This seems about right. How much ram? My system pulls from 160-200W when 9 drives are spinning, but I also have 8GB of ram and an i-RAM ramdisk. Link to comment
jimwhite Posted October 6, 2008 Share Posted October 6, 2008 Another thing to consider is the power supply design. Ideally you want a "single-rail" power supply, that is it has a single 12volt supply, not two or three. I had an OCZ 650 watt supply with two rails. One supplied the mother board, one supplied the peripheral (drive) cables. It supplied less current to the drives than an older single rail 430 watt supply. With the 650, all was well until I hit the button to spin-up all (10) drives from spin-down. The server would reboot! I've since replaced it with a Corsair 750w single rail supply, it happily will spin up 14 drives, and is >80% efficient from 20-100% load. Link to comment
yodine Posted October 6, 2008 Share Posted October 6, 2008 I have 12 drives and a core 2 duo 3GHz and the max Watt it took was 325W, of course at startup. But all drives awake, it will eat less than 200W and will go down 79W when all the drive spindown. This seems about right. How much ram? My system pulls from 160-200W when 9 drives are spinning, but I also have 8GB of ram and an i-RAM ramdisk. I have 2x1Go RAM, but i think to switch to 2x2Go RAM for the file structure to stay more in cache Link to comment
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