[mythtv-users] apc backup

[Simon Hobson]

David Williams <mythtv_david at yahoo.com> wrote:

> I'm posting to this group v. APC since my issue is mythtv-related.
> 
> Spring rains generally manifest in power outages in my area with disastrous consequences. On more than one occasion my hard drive has been corrupted to the point where with my existing skill set I found it impossible to resurrect. It seems like BIOS was more forgiving than UEFI.

Different filesystems are more forgiving than others - but I've generally had few problems with EXT3 (yes I'm a bit old fashioned !) which will generally recover by just rolling forward the journal. Other tricks can make problems "less troublesome". For example, while it's one of those hangovers from the days of LILO and BIOSes that couldn't access past a few hundred meg of disk, having a /boot on it's own filesystem should generally mean that you can get to a busybox shell if your root filesystem is damaged. From there, fsck will usually get your root filesystem going and from then on things get easier.

> In an effort to head off another round I purchased an APC 750 Backups. I set this up with the apcupsd app and it shuts down just great. My question is this: I used the stock settings with the exception of Battery level which I changed from 5 to 30. I welcome any and all advice on these settings. 

Ah, the "how long is a piece of string ?" question. It's a trade off really ...
If you have frequent short power cuts, then you want to stay on battery for a while and have a chance of not having to shut down. On the other hand, if your power cuts are usually longer then you might as well shut down fairly quickly and conserve battery life. The battery only has a limited number of cycles, and this is fewer if you deeply discharge it, and significantly more if you only part discharge it - so from a battery life POV it's best to shut down with plenty of capacity left.

So it's well worth keeping a log of power cuts so you can get a better feel for how long and how frequent they are - and if they are clustered*. Based on ow long your UPS will maintain the system, you'll then be in a position to decide whether you generally want to try and ride out the cuts, or shut down fairly quickly.

* Often the power may come back on, only to go off again very quickly, and may do this several times - so the battery won't recharge before the power goes off again. That's why the UPS has a setting to not turn on before the battery has reached a certain level.

But there is no "right" or "wrong" answer here - just different variations of compromise. One ideal is to have enough battery capacity to ride out any likely power cut - but that's expensive to have around, especially if you don't have many power cuts.

Oh yes, and consider what else your system needs to operate. For example, if you are going to keep your system going through a power cut, then you may want to consider having anything it needs (for example, aerial amplifiers) to continue recording powered off the same UPS. Otherwise your system keeps running, but recordings fail - of have a blank bit in the middle.

In business, I've often seen a UPS (sometimes a very expensive one) that doesn't support everything. For example, I recall looking at an expensive phone system, with an expensive UPS supporting it - but across the room, the terminal unit for the phone lines plugged into a wall socket !
Similarly, often the internet router, or a network switch, gets forgotten about.