I think I know the answer already, but I'll ask it anyways just incase... is a hot restrike bad for the ignitor on a magnetic ballasted Metal Halide fixture?
I assume it's bad for both magnetic and electronic, but I'm mainly focused on magnetic for now since I'm new to the magnetic ballasted Metal Halide fixture gang.
... never owned a magnetic Metal Halide fixture until I recently bought 6 MH fixtures for my garage.
I've only gotten all of them to hot restrike one time.
... I also assume that leaving the fixtures on for a very short amount of time, and only turning them on when entering the room, is bad as well.

Hot restrikes are not "encouraged" situations, but they do happen and manufacturers take it into account when designing ballasts and ignitors. However, if you abuse of it, lets say multiple hot restrikes every day, you'll wear out both the lamp and the ignitor (and eventually maybe the ballast, but it is normally quite resistant).

Take for instance metal halide (or HPS for that matter) in a streetlight, atop a pole. If the power dips or cuts out momentarily at night, a hot restrike will happen and is not really avoidable.

HID lamps are normally (=officially) designed with at least 10 hours per start, save a few power outages or inadvertently turning off a switch. So yes, turning them on briefly every time you enter the space will wear them out prematurely.

I have a few metal halides in daily use in my home. They get about 1-2 starts per day, running at least 2 hours each time, more in winter and less in summer. The lamps and ballasts have held up quite well with practically no failures.

Normally lamp EOL cycling causes way more hors the ignitor is running, so are way stronger contributor to its wear than a few hot restarts and the components still have to be designed to handle that with a reasonable operation lifetime. But it definitely wears things out. The ignitor, the ballast if exposed to the high voltage (superimposed ignitors are better from that aspect), the wiring insulation, socket (the high voltage promotes effect called Time Dependent Dielectric Breakdown, essentially ionizing and shifting atoms in the structure, causing micro defects which then become weak spots, so the complete breakdown happens after some time). That means the insulation can handle the high voltage pulses for some time, but when too long, it breaks down. So when the ignitor never sees a bad lamp, it stresses the thing for barely few seconds over the complete 40 year service life, but if e.g the lamp is out, it accumulates hours of stress within a month...

Here I think the electronic ballast would be more OK with frequent hot restarts than common ignitor on a magnetic ballast. The reason is, the electronic ballasts use to have functions detecting too long pulsing and shutting down for a few minutes before repeating the starting attempt. Plus it uses to feature cycling EOL detection, shutting the ballast too. The main objective was to limit the lamp wear (situations when there is just a thin spark from the ignitor but the lamp does not start yet) and/or prevent annoying operation (the cycling) or lamp explosion at the lamp EOL, as a side effect it significantly limits the time the ignitor is active, so limitting wear of its components.
Plus electronic ballasts tend to use mosfets for the switching of the high current pulses (the primary of the ignition step up transformer), rather than breakdown triggered SCRs (the sidac,...), which do handle the high currents with way less wear out.

There are ignitors for "magnetic ballasts" that have similar functions, but it means extra cost (almost double for a superimposed type) unlike with the electronic ballasts where the processor is already present for other reasons, so can do these functions essentially for free.

@Sol, I plan on running all of my Metal Halides much more during the winter time. Especially since I'll be spending more hours in that garage to
winterize my vehicles. There's also a few more lamps that I plan on replacing, with lamps made by more reputable companies like Sylvania, Philips, etc.
I'm making plans on buying replacement fixtures as well, just incase, since they seem to be really cheap on Ebay... although... I don't know if cheap
fixtures = cheap components. If the components prove to be cheap, I'll probably end up switching to different types of Metal Halide wallpacks.

@Medved, this makes me wonder if the electronic ballasted CMH 20w tracks lights I have, fit your description in terms of the start up characteristics.
They do definitely take a couple of minutes before attempting to successfully strike again. You can hear it, even when it's a cold start.
I think my Par38 23w GE self ballasted CMH do this as well but in a noticeably different way... especially during hot restrike.

Elecronic ballasts for HID lamps, are significantly different than electronic ballast for fluorescent lamps. They don't strikes from the ballast OCV, but from an ignitor incorporated inside the ballast casing.

Dor, at no point in the thread were fluorescent ballasts mentioned, so why do you see the need to bring them up.?? 

Yo... wait... what?  I'm so confused. No one mentioned fluorescent ballasts. Although fluorescent lighting is my favorite source of lighting among
all sources, I made sure not to bring up fluorescent lamps, or fluorescent ballasts, in this thread. Am I missing something? lol

Coming back to HID electronic ballasts, most have a timer and will stop trying to start a lamp after a set time. Usually after 2 minutes, it will wait 5 minutes before trying again. This cycle will repeat for about 20 minutes and if still unsuccessful, it will shut down the ballast completely until power is cycled. This is why the label says to cycle the power upon lamp replacement.

Most ignitors for magnetic ballasts will pulse continuously until the lamp strikes, the power is cut or something else fails.

Just a personal viewpoint, I don't like to deliberately hot-restrike lamps. Firstly, it has an effect on lamp life, secondly it may possibly damage the control gear, and lastly I just don't see the point.

If you get a momentary power glitch, then how long the lamp takes to restrike is important, which is why I'm rather partial to twin arc tube HPS lamps (and testing one of those is the only time I would do a deliberate hot restrike) but otherwise, no.

That's just my 2p's worth, YMMV as they say.

Yeah I'm learning about this, which is why I created this thread: I don't like to hot restrike my MH either. Definitely seems like a lot
can go wrong when doing so. I *might* hot restrike my 6 MH's in my garage for video purpose only at some point, (one video) but that will be it.
Mainly when each fixture officially contains a different style bulb from different companies. I'm still working on that. lol
I haven't necessarily been the best in terms of my 20w CMH track lights though. I've had those hot restrike many times over the last few years...
proof that what Medved said is correct... so far it does seem like electronic MH gear handles it well. I've had those fixtures in use daily since 2015.

I only deliberately hot restrike lamps and fixtures when I acquire them as I like to know how long they take. Otherwise, it only happens either if there is a momentary power interruption or by error (such as unplugging the wrong cable). Neither happens very often so I don’t worry about it.

Speaking of hot restrikes, I have a 35/39 W magnetic ballast running a CMH lamp and it does not hot restrike. The lamp cools down enough to have a partial discharge and that’s it. Somehow it has an equilibrium in which it is cool enough for the partial discharge and it keeps it from cooling enough for a proper strike. All the while, the ignitor is buzzing away. I have to turn it off for 10 minutes or so and only then will it strike. I need to test out other (different) ignitors but at the moment I am lacking the time to do so. Needless to say that I don’t let it run when no one is home.

@Sol, that brings up another question that I've been wondering... what is the lowest wattage magnetic MH ballast? If I can somehow find a wallpack version,
I... might add that in my garage as the final light. Maybe. That's a very tough call because it's definitely bright enough in there... but I'm a lighting
enthusiast. I can't help it.
I probably wouldn't buy that wallpack anyways, because I've made a vow not to buy wallpacks that run MH lamps horizontally, and it seems like most wallpacks
run them horizontally.
But yeah, I did hot restrike my 6 MH wallpacks in my garage, and the only two MH lamps that took the longest to start, were the Sylvania and the CMH Philips lamps.
The Sylvania took the longest time of the two, but both of them took almost 10 minutes to restrike.
The GE MH, to my surprise, took less than a minute to restrike. So it's like those wallpacks seem to work the best with GE lamps. Warm up time is also
the fastest with the GE lamp as well, which reaches full brightness in much, much less time compared to the others.

Speaking of hot restrikes, I have a 35/39 W magnetic ballast running a CMH lamp and it does not hot restrike. The lamp cools down enough to have a partial discharge and that’s it. Somehow it has an equilibrium in which it is cool enough for the partial discharge and it keeps it from cooling enough for a proper strike. All the while, the ignitor is buzzing away. I have to turn it off for 10 minutes or so and only then will it strike. I need to test out other (different) ignitors but at the moment I am lacking the time to do so. Needless to say that I don’t let it run when no one is home.

I know ignitor tend to prolong the cool off time (by essentially feeding some small power), but to completely prevent the lamp from cooling off to successfuly restrike, that is wild. It even does not sound to me like being OK.
To me it looks like a too low ballast OCV (so not able to build a fat arc in time after tge arctube gets ionized) and/or too high ignition peak voltage (causing ionization breakdown way before the lamp cools enough to allow the OCV to form a thick fat arc).
From your personal info I see "120V 60Hz", so I assume the ballast in question is a HX transformer with a semiparallel ignitor.
There all the important parameters for the ignition, like the OCV and the peak ignition voltage are formed by the ballast itself, so it is strange it clearly does not match the lamp.
Wonder if you can get some lower energy ignitor. If the voltages are not exactly tight, at least the ignitor won't have enough power to keep the arctube warm.
Of course, "timed ignitor" (that uses to be their name here; similar timing pattern as you got with an electronic ballast, just controlling only the ignition pulses generation) would be the best way to go, but I've seen those offered only for European ballasts. So either makers for the US market gave up on it (with the complete electronic ballasts filling that need), or such features are used only for some ballast models (as ignitors in the US tend to be rather proprietary part of a ballast, not a separated standardized commodity like in Europe, so there is no need to describe the exact features of various ignitors), or such features are labeled in a different way.

@Medved : I intend to get a superimposed ignitor some day. I have one in a 70W remote ballast setup where I completely removed the ignitor from the ballast enclosure and have it with the lamp. No issues with that one. I find that European superimposed ignitors do work with North American ballasts because they are wired on the OCV side and get enough volts to work. The one that is there now is the one that came with the ballast kit. I have other ones that I could try just to see if it’s this particular one or not.