[arm-allstar] Some points on update failures the very few who experienced them

[Doug Crompton]

I need to make some points regarding updates. We had at least 1000 update
downloads of the Kernel update several weeks ago. A couple failed. a small
fraction of a percent. I personally updated 15 nodes locally and remotely
without any problems. Updates are important, they fix bugs and add
functionality. A Kernel update, and we have had a few, is a big update. It
takes longer and writes a great deal more to the SD card. SD cards if you
are using good ones are very reliable. We recommend Sandisk Ultra. Don't
buy some strange name card at the drug store! That being said SD cards
don't last forever and can in rare cases be corrupted. They don't last
forever and in critical situations you should always have a spare on hand
that can be swapped in very quickly. When we did put out the Kernel update
I recommended that users backup their servers. Most users make few changes
to their configurations so backing up may not be required. It would be easy
to re-setup the image. Others make a lot of changes and backing up
periodically is a good idea. You can buy a 32G or better USB stick and
leave it plugged into your Pi and use the file-backup.sh script to do this.
It will make multiple dated backups that you can later returned to if
required using the file-restore.sh script.

Another big problem among the Pi community is the use of inadequate power
supplies. Of all the reported Pi problems this is the number one culprit.
The Pi, especially the later Pi3's require more current and all Pi's can
have high instantaneous current draws when the processor ramps up in speed
or if it is in turbo mode. Writing the SD card also requires more current.
It is the users responsibility to ensure that they are using an adequate
power supply. A 5V charger from some other device you have laying around is
NOT adequate. Like any computer the Pi requires adequate and clean power.
The Pi2 requires at least a solid 2 amps and the Pi3 2.5 amps. This does
not mean the Pi draws that much average power but it needs the reserve
during high CPU usage. This usage could not in most case be measured on a
meter, it would take an oscilloscope to see the instantaneous demands.
Although I use good wall-warts and I have had no problems they can be
problematic both in supplying adequate current and being clean. I have seen
wall-warts wipe out HF or cause audio noise on a Pi server. The 12+ volt to
5V 3A encapsulated car regulators work very well and would be ideal where
you have 12 volts available.These are available from multiple sources on
Ebay or Amazon.

Also it is important, as it would be on any computer, to use a UPS. Often
power outages can have surges or multiple on and off cycles over a short
time frame. This is the kind of thing computers do not like and it could
corrupt an SD card. A UPS would certainly help to guard against this.

Another small thing you can do is check for obvious errors on your SD card.
You can't fix a mounted card but you can check to see if there are errors:

e2fsck -n /dev/mmcblk0p2

e2fsck 1.42.13 (17-May-2015)
Warning!  /dev/mmcblk0p2 is mounted.
Warning: skipping journal recovery because doing a read-only filesystem
check.
/dev/mmcblk0p2: clean, 77662/243360 files, 461927/972182 blocks

If you do have errors they could be recovered but you would have to do that
on a PC running Linux by inserting your SD card into a reader/writer.

While we can't control how users manage their systems if you take the above
measures with your Pi's it would go a long way towards ensuring a long and
stable life for your servers. I want to stress again the importance of
doing updates and the fact that there is an extremely low failure rate when
doing so.


*73 Doug*

*WA3DSP*

*http://www.crompton.com/hamradio <http://www.crompton.com/hamradio>*