Re: RAID HDDs spin up sequence

[Roberto Spadim <roberto@spadim.com.br>]

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
don´t 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, don´t start
server. that´s 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@nexgo.de>:
> 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
>> (it愀 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
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-- 
Roberto Spadim
Spadim Technology / SPAEmpresarial
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