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I have two identical Nexus 7 (GSM) devices. Both running Android 4.4.4, KTU84P.

Now one of them shows that Lollipop 5.0.2 is available as OTA, but the other one says that no updates are available. How is that possible?

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OTA updates that come directly from Google (such as Nexus devices) are rolled out in waves. An excerpt from Dan Morill's comment states that, specifically:

Rollouts are conducted in phases. Typically they start at 1% of devices for around 24 - 48 hours; we watch the return rates and resulting device checkins and error reports (if any), and make sure nothing looks wrong before sending it to more. Then typically it goes to 25%, 50%, 100% over the course of a week or two.

What the percentages mean is that when your device checks in, it has a 1% chance (for example) of being offered the OTA. If it doesn't (randomly) get an offer, it will never get an offer until the next batch.

Since the Lollipop update for the GSM Nexus 7 just began yesterday, one of your devices was likely chosen for this "wave" and the other was not. If you want to update manually, you could try to find a copy of the OTA and attempt to sideload it or use the proper factory images.

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  • Alright, for some reason I thought it would be country specific rollouts or something like that. So it's probably just some algorithm that checks some identification from the device before answering wether it has updates.
    – vertti
    Feb 3, 2015 at 16:10
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    It's basically just random. I updated the excerpted quote with the next paragraph, which explains the selection process. When your device checks in, it randomly gets either a yes or no. To start, it's a roughly 1% chance of a "yes". If it gets a "no", Google will record that, and every subsequent check will also be a "no" until the next wave starts, at which point a check will result in another random yes/no (with 25% chance of a "yes"). The probability that you get a "yes" increases with each wave, up to 100% at the end.
    – eldarerathis
    Feb 3, 2015 at 17:07
  • Basically, if the numbers are truly accurate and not just for the purposes of an example, you had a 1/10000 chance of both devices getting offered the OTA during the first batch.
    – eldarerathis
    Feb 3, 2015 at 17:09
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    @SixthOfFour that may well be the case for Samsung OTA's as they control the rollout. This question (and answer) are specific to how Google rollout the OTA's to their devices. I'm not aware of any definitive information on how other manufacturers handle updates.
    – bmdixon
    Feb 3, 2015 at 17:25
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    @SixthOfFour I've clarified the first sentence slightly to try to make my intent a bit clearer, but yes, this really only applies to Google's update strategy as bmdixon notes. Carriers can also affect this, since they have a great deal of influence over OTA timings and rollouts. The statements I've referenced come from one of Android's engineers, so I have no reason to doubt their accuracy in this instance, but I would not be able to gauge whether or not they apply across the board to every Android device.
    – eldarerathis
    Feb 3, 2015 at 19:17

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