[kwlug-disc] How much CPU to keep a disk fed? [Was: Re: Which vendor for Raspberry Pi kits?]

John Van Ostrand john at vanostrand.com
Tue Dec 10 13:23:24 EST 2013


Be aware that Raspi is failrly slow at CPU and with external connectivity.
I expect it may be fine for DLNA but if you have to move a lot of data to
it often you may find the 100MB/s Ethernet is too slow.

I have three RasPis running here at home and I have to remember the power
savings I'm getting because they are slow compared to the speed of a
full-blown server.

That said, I'm all for the idea of putting low-end services onto a Raspi.
Currently I'm happy with Asterisk running on it. I have a web server on
another. Drupal page loads are about 3 seconds. My Perl-based wiki is much
slower. But since they hardly see any hits I'm happy with slow performance.

I tried a disk-server on Raspi, in fact it's still in place but I'm not
using it. The real problem with disk and Raspi is that USB2 is too slow for
the disk but the real bottleneck is the 100MB/s Ethernet. I'm more in
favour of using a WDC MyBook NAS which supports NFS and costs about the
same as a USB disk. You're not running Apache on it without hacking it
first though and I don't know of any rooting options.

There are other hardware solutions that are low power but have higher-end
connections or other faster features. These are much more expensive and
don't have the community that Raspi does. So I stuck with Raspi.

I keep a spare Raspi and spare power bricks for hardware failure. It's
still cheaper than a server and I can handle a little down time in case of
failure.


On Tue, Dec 10, 2013 at 5:07 AM, unsolicited <unsolicited at swiz.ca> wrote:

> Good info, but meant CPU (horse)power, not electrical power. (-:
>
> - was expecting GHz not mA. (-:
>
> On that electrical power ... less need for usb hub power if external usb
> (enclosures) are powered?
>
>
> On 13-12-10 02:25 AM, Bob Jonkman wrote:
>
>> unsolicited wrote:
>>
>>> Just how much CPU power does it take to keep a (USB? eSata?) disk fed,
>>> anyways?
>>>
>>
>> A USB socket is required to provide 500mA. If you plug a USB extender
>> into computer, that computer's USB port can only supply 500mA for all
>> the ports on the extender (and the extender itself). That's fine for a
>> thumbdrive or two, but if you're trying to use an external, spinning
>> disk you'll need an extender with a power supply.  I've got a couple of
>> 5+ year old external USB drives for which the cables have double USB A
>> connector, one for data+500 mA and the other for another 500 mA.
>>
>> Don't know about eSATA, but on my computer the USB 3.0 port and the
>> eSATA port share one physical connector (ie. I can use either USB or
>> eSATA, but not both at the same time). So I suspect eSATA has the same
>> 500 mA limit. OTOH, my external eSATA drive has its own power supply.
>>
>> I was reading earlier this week that the new USB spec will supply up to
>> 5A at 12V, which seems ridiculously high.
>> http://www.zdnet.com/new-usb-plug-coming-good-news-bad-news-7000023935/
>>
>> --Bob.
>>
>>
>>
>> On 13-12-09 11:17 PM, unsolicited wrote:
>>
>>> Just how much CPU power does it take to keep a (USB? eSata?) disk fed,
>>> anyways?
>>>
>>> (Guess it depends if you're running something checksumming, like BTRFS,
>>> I suppose, too?)
>>>
>>> I've seen some mirroring (striping?) external USB boxes, but I wonder if
>>> catching a multi-GB rsync feed nightly would be beyond a Pi.
>>>
>>> Note: My question, not Khalid's. Different beastie.
>>>
>>> Are there other 'Pi' beasties out there?
>>>
>>>
>>> On 13-12-09 10:22 PM, Khalid Baheyeldin wrote:
>>>
>>>> I am considering building a small server that would have a largish USB
>>>> disk. The server would be rsynced from the main server, and runs
>>>> minidlna
>>>> for access to photos, videos, music, ...etc.
>>>>
>>>> The Raspberry Pi seems like a good platform for this, being low power
>>>> and
>>>> runs Linux.
>>>>
>>>> Online sites are selling kits that include a power supply, SD card
>>>> preloaded with NOOBS, and a case as well.
>>>>
>>>> So, the question is, anyone here order Raspberry Pis? Where did you
>>>> order
>>>> it from? Canadian or USA based? Did they ship on time? Did you pay
>>>> customs?
>>>>
>>>> Looking for experiences, sites to avoid/recommend, ...etc.
>>>>
>>>> Examples I saw are Amazon, and this
>>>> http://canada.newark.com/raspberry-pi-accessories
>>>>
>>>>
>>>>
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-- 
John Van Ostrand
At large on sabbatical
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