In message , Martin Gregorie
 writes
>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.
>
>

It is in an external enclosure powered by a wall wart.

3.5" disc WD red 3 years old.  Connection is via USB, the disk's
enclosure has an adapter built into it.

Adrian
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