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 -- 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
