On Wed, 19 Jun 2019 18:55:43 +0100, Adrian wrote:

> In message , Lew Pitcher
>  writes
>>Adrian wrote:
>>
>>> I'm looking into getting a small UPS, that will handle a PI and an
>>> external disc drive.  We seem to be a bit prone to very short power
>>> outages (~1 minute), but this is causing problems with remounting
>>> drive when the PI reboots.  Longer term power outages I'll live with.
>>>
When you say the disk is mains powered, does that mean its in an external
enclosure with either a mains socket on the enclosure or a wall-wart
feeding low voltage DC into its enclosure?

And, of course so we can see what its power requirements are:

- What type/model/size is the disk drive and how old is it?
  Age can have a bearing on its power requirements and size
  (2.5"or 3.5") definitely does. [1]

- How is it connected to the RPi? IOW is there any interface device,
  such as a USB adapter that also needs to be powered.

[1] A quick check shows that WD Blue 3.5" drives have a peak power
requirement of around 2A at 12v (20 - 24 watts) while WD Blue 2.5" drives
have a peak requirement of 1A at 5v (5 watts), which, of course has to be
added to the start-up power needed by the RPi when considering what peak
load the UPS must be able to handle. It probably also affects the
capacity vs. length of power outage that can be supported by your chosen
battery capacity, because a disk that can spin down when idle probably
uses less power than one that has to remain spinning while the system is
running - unless, of course the applications you're running has a
pathological activity pattern that lets the disk time out and spin down
and then almost immediately spins it up again for the next active period.


--
Martin    | martin at
Gregorie  | gregorie dot org

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