source code is the best source of information try here too (WIKI) https://raid.wiki.kernel.org/index.php/Main_Page 2011/1/31 Roberto Spadim <roberto@xxxxxxxxxxxxx>: > the better probability here is: all disks must be waked up > since you can have acces of 1gb but starting at a position that all > disks must be used > donÂt try used small PSU > HP Proliant ML310G5 start all hardware on power up (a lot o Watts) and > after slow down thinks... why? check if PSU is ok, if not, donÂt start > server. thatÂs a good PSU system. > ok if you want to test, i think the worst scenario is all disks beeing > waked up, i think linux use async (many threads) commands to send > write/read, maybe you will have a small time between wake up (maybe > just some microseconds) > > 2011/1/31 Piergiorgio Sartor <piergiorgio.sartor@xxxxxxxx>: >> On Mon, Jan 31, 2011 at 07:09:24PM -0200, Roberto Spadim wrote: >>> you psu must be dimensioned to work with everythink at full work load >>> (itæ a real production NAS right?! not a test) >>> your SAS/IDE/SATA controller and HDD manual should be checked >>> how hdd wake up? one command (read/write) over sata/sas/ide channel wake it up? >>> on linux raid we have a read algorithm and a write algorithm >>> if a raid1 write occur all disks will wake up >>> if a raid1 (raid0 or another) read occur only the disk will wake up >>> >>> but check you SATA/IDE/SATA controller, how it wake up your disk, and >>> how you hdd wake up >> >> Hi, thanks for the answer, unfortunately I was >> hoping to have made myself clear enough. >> >> First of all, it is a RAID-6, so let's say that's >> already decided by requirements. With SATA HDDs. >> >> Second, the question was exactly about how the HDDs >> are waked up. This is a SW issue, trying with normal >> setups, i.e. a couple of disks, it is possible to >> send them to sleep (hdparm -y /dev/hdX) and the wake >> them up by a simple access. >> I had no opportunity to check this with a RAID-5/6, >> so I was asking if anyone knows. >> >> Finally, in order to be power efficient, the PSU, >> assuming something like an 80 Plus Gold, should work >> at not less than 20% of the nominal power, otherwise >> (according to some reviews), the efficiency drops far >> below the 80%~90% declared by the 80 Plus standard >> (which is measured at 20%, 50% and 100% of the maximum >> specified power). >> It seem it gets easily around 40%~50%. >> So, the PSU must be somehow under dimensioned for the >> spin up of 10 HDDs, which seem to require a possible >> 30W*10=300W (some nasty HDDs seem to require 30W, in >> this situation) only for the storage. >> >> If the HDDs spin up one after the other, then the peak >> consumption is only 30W, which might allow a lower >> power PSU, in contrast with the requirement to provide >> 300W alone for the spin up. >> >> So, back to the original question, if a 10 HDDs RAID-6 >> is in standby, how do the single HDD will be waked up, >> in case of access? Of course, a quite larger access, >> i.e. some GiB of data. >> >> Thanks again, >> >> bye, >> >> -- >> >> piergiorgio >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-raid" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at Âhttp://vger.kernel.org/majordomo-info.html >> > > > > -- > Roberto Spadim > Spadim Technology / SPAEmpresarial > -- Roberto Spadim Spadim Technology / SPAEmpresarial -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
