[Google Pixel 2 XL Questions & Answers] simplepinoi177:
Thank you [MENTION=4670411]Az Biker[/MENTION]! You are the best! You don't know how flattered I am that you even kept me in mind, let alone be among that great list...I am truly humbled...

So, hascherpur, I'll answer a bit of your questions, then I'll offer you some general advice when starting up with this Pixel 2 XL (taimen) as well as some dire tips if/when you get yourself in trouble (as Az Biker had alluded, it seems with this device, it is rather "inevitable" ;):good: )...

TWRP (and most other flashing installation files/process [ROMs, Magisk, etc.]) actually consider and keep in mind the multi-slot possbility and have made it that, if it's called for, it will automatically patch/boot/load either/both/individual slot. You'll see many and mmaannyy others go about manually/forcibly "set[ting]" and choosing specific slots, but I, like Az Biker, in my (roughly) 16 months of using this device have never, ever found a reason to -- and, for better or worse, I've broken my taimen and my gf's walleye countless times and managed to save/recover it but completely got it bricked twice.

The time you need to extract those (bootloader, radio, vendor, etc.) is when you're updating or reparing/recovering your device. A note about that though: if you wish to manually update our device (monthly; for the security updates), the absolute best way to go about it is to download the Full Factory image direct from the Google Developer's website, and extract the files within the .zip (usually these bootloader, radio, vendor, and others totalling usually 9-ish files) into the folder that has adb.exe and fastboot.exe, modify/edit the "flash-all.bat" file/script (flash-all.sh depending on your OS) and remove the "-w" (unless you wish to "w"ipe your internal), and then run that flash-all file. Because this manner of updating essentially re-installs the /system and /vendor folders and partitions, this would actually be more of a "clean" flashing than the other methods; downloading the OTA (not Full Factory) image and manually (via adb) updating and/or modifying your device so it will take an OTA update -- which is it's own hairpulling and (imo) unnecessary process -- these methods should be considered "dirty" flashing/updating, if anything.

I'm unsure how HavocOS ROM updates and if it needs to be done within its own environment or in the recovery, but I imagine much of what I just said would still apply, at least in some manner.

Okay, some general info you would find helpful and would (hopefully) keep you from falling into some of the "pitfalls" that we've all run into and have told ourselves "...if I had only known beforehand...". There is the fact that, for all Pixels -- and I'm pretty sure any multi-slot device -- there is no more recovery partition! It now resides in & with the boot partition/image. This has thrown so many new users of Pixel phones for a loop...they're usually attempting to "flash to recovery" for 24 hours before finding this out :silly:. Then there is ALL the issues you'll run into with adb, fastboot, and platform-tools in general; When you get issues when using adb and/or fastboot, you're initial instincts is going to lead you into thinking something is wrong with the image, device, and/or commands -- and with this/our phone, many times that is not the case (believe it or not, it'll put up a flashing-type error, but it's actually the USB cord?!)! Az Biker has the best troubleshooting guide in his signature, and it holds advice that usually gets things working 90% after having issues -- some general tips to keep in mind is make sure you

UPDATE

the platform tools and sometimes, for some reason, you have to run the same commands/process 4-5+ times before it "...works all of a sudden, this time...!" But, basically (as Google is genius in this), as long as you have access to Bootloader Mode, then there's always hope! I've gone as far as re-formatting partitions, changing the partition type, changing the size of the partition, and even manually flashing 12+ image files after forcing the partition size to change for those image files, and I've been able to come back from it because of being able to have access via Bootloader Mode.

Now, being able to unlock the bootloader and have a custom recovery, especially considering you plan on flashing custom ROMs and/or kernels and such,

IT IS BEST THAT YOU MAKE A BACKUP (NANDROID IS BEST)!

I know that this isn't exclusive advice for the Pixel 2 XL, but it still bears reminding; but here's some taimen specific advice -- keep in mind that many backup processes (TWRP specifically) does not (normally*) backup the data in your /internalsd (which includes your Download, Music, Photos folders)! (*i say "normally" because there is a convoluted method I've found that actually does backup the internal sd which I do every month, which I could walk you through if you are interested...). But I believe it's the best backup method because it at least backs up the system, boot, and data partitions -- note: you don't have to replace and install the custom recovery in order to utilize it; there is always temporarily booting the twrp "image" and running it off that -- but there is also TB and the other myriad ways to backup as you see fit (I'm completely unfamiliar with HavocOS, but there might even be a backup method via its environment). The key thing is: that you make backups!

And, lastly, some specific advice for when you run into issues... Re-installing/Re-flashing the Full Factory image is always a great way to fix a lot of the issues out there -- I still remember the days of my Galaxy S5 and Motorola Droids where "flashing" would wreck and wipe all data and customizations, so I love how Google made it so that's not the case with the Pixels -- but if you find that it hasn't resolved the issue, using Deuce's script (that can be found HERE) has saved countless many in repairing and recovering our devices. One of the greatest things about it is that it manually and individually flashes each and every image file to BOTH slots! Thereby covering a lot of "little bases" that a standard flash-all script doesn't do -- the only caveat is that you'll have to additionally extract all 15+ image files from the image .zip file (that resides within the Full Factory .zip file). One last recovery bit of advice, running the command "fastboot getvar all" will provide a great deal of pertinent information about the device, to say the least! It'll be good if you wish to check and to include when requesting help...

My deepest apologies for making this as long as it is; for those who know me, sometimes I can't help myself. Well, there's really that many crazy things that would be so helpful to know at the beginning with this device as well as I type very fast and fluently (kind of as fast as I talk), so I get away from myself...In any case, thanks for reading this far, if anything, and my sincerest apologies...

Again, I'm very happy to help and so glad the Great Az Biker had thought of me to include. This is a wonderful, great device and I don't want any other! But, as with all great things and loves, it will also have its "hair-pulling" headaches...so, just take your time and read and re-read, keep some of these things in mind, and good luck to ya!