Re: RAID HDDs spin up sequence

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

i think yes (hd wake up on write/read command)
check linear and stripe layout
linear is like a lvm (concatenation)
i think raid0 work like stripe, but need to check it and return (raid0
= 0 = stripe level,  linear!=raid0 for linux implementation)

2011/1/31 Mathias Burén <mathias.buren@gmail.com>:
> On 31 January 2011 21:25, Roberto Spadim <roberto@spadim.com.br> wrote:
>> just if you need information on all disks
>> define your read. are you reading 1 byte or many bytes (on all hds?)
>> the number of bytes read/write is the point
>> if you need another disk to read/write you need to wake up your another hd
>>
>> check this implementations on mdadm:
>> linear, raid0, 0, stripe
>> maybe one is better for low power than another, but maybe one is
>> faster than another
>>
>> 2011/1/31 Mathias Burén <mathias.buren@gmail.com>:
>>> On 31 January 2011 21:09, Roberto Spadim <roberto@spadim.com.br> wrote:
>>>> you psu must be dimensioned to work with everythink at full work load
>>>> (it´s 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
>>>>
>>>> 2011/1/31 Piergiorgio Sartor <piergiorgio.sartor@nexgo.de>:
>>>>> Hi all,
>>>>>
>>>>> assuming there is a NAS, with, for example, 10 HDDs
>>>>> in RAID-6. Assuming the HDDs are put in standby, in
>>>>> order to save energy, when the NAS is not used.
>>>>> How is the spin up sequence when the corresponding
>>>>> /dev/mdX device is accessed?
>>>>> Will the system spin up one HDD at time or all together?
>>>>>
>>>>> Obviously, one at time will limit the peak current,
>>>>> thus allowing a better dimensioned PSU, working almost
>>>>> always around the optimal efficiency point.
>>>>>
>>>>> Thanks a lot for any information on the topic,
>>>>>
>>>>> bye,
>>>>>
>>>>> --
>>>>>
>>>>> piergiorgio
>>>>> --
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>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Roberto Spadim
>>>> Spadim Technology / SPAEmpresarial
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>>>
>>> I would guess, that on a RAID0 setup, any read to that md device would
>>> wake every disk up in that setup. No?
>>>
>>> // Mathias
>>>
>>>
>>
>>
>>
>> --
>> Roberto Spadim
>> Spadim Technology / SPAEmpresarial
>>
>
> I meant "default RAID0 setup with mdadm", with a minimum of 2 HDDs,
> and any fs on top of that. (with or without lvm)
>
> Unless the file is very small (smaller than the minimum piece of data
> that's being spread across all devices in the RAID0 setup (btw, that's
> this called in RAID0, is it chunk size? Stripe size?)) or cached,
> you'll wake the HDDs up. Right?
>
> // Mathias
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-- 
Roberto Spadim
Spadim Technology / SPAEmpresarial
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