win10/win7 dual boot (hardware option)

On my desktop I am using ICY DOCK SSD cage for my OS:
MB322SP-B_ExpressCage_2.5" HDD/SSD CAGES_ICY DOCK manufacturer Removable enclosure, Screwless hard drive enclosure, SAS SATA Mobile Rack, DVR Surveillance Recording, Video Audio Editing, SATA portable hard drive enclosure
One tray is dedicated to one OS (either Win7 or Linux), the other is for Win10.
I run whatever OS I want while the other OS and it's SSD is disconnected.
All data files are on NAS.
I have used this setup for a while for Win7 and Linux with no problems at all.
Now I am trying to use it for Win10 as well.
Initially everything was OK, but couple of times I have had problems with Win10 where it wouldn't boot.
Problem was solved with changing boot sequence in BIOS, but... it has me worried (I know little about Win10).
Why should it be? Is there something different about Win10 that is causing it?
Win10 version 1909 (build 18363.418)

HI,
Fast start features and or hibernation features on 10 mess up dual/ tri booting plus 10 acts like an alpha when it's mostly beta
Good you remove other os's this should solve many issues with dual.. with 10
Is there any shared data drives you leave connected there must be if you have to change boot disk order ?

Thanks!
Yes, there is a shared network attached storage which is common for all these different OS.
This is normally ON all the time - it has never caused any problems previously, but that was before Win 10...
Although I have noticed that Win 10 doesn't auto connect at boot anyway? so I have to click on it to open/connect manually (which I am OK with).
There is no other HDD for storage on the PC, only OS SDD.

Hi,
Okay yep even win-7 might freakout a little if it reads writes it did not write on a connected/ shared ssd or hdd
10 is just over reacting to changes likely

10 does usually auto mount attached storage devices so yeah sounds like you have it not doing that.
I'd just confirm in your bios that secure boot and fast start is disabled for starters.

Hi,
I've been using one of these for a while one slot for os the other for data makes life so much easier
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1

fast boot and secure boot - both disabled

Yes, I have done multi-booting various OS before, but it gest very messy if you do more than a couple, plus windows gets very possesive and can cause problems.
"Mechanical" multi boot of swapping drives has a lot to recommend it (at least AFAIAC).
It makes life so much easier indeed.

My PC has UEFI dual Bios and it gets very strange with booting priorities.
For example Win 10 seems to only boot if "boot option #" is set to (in my particular case):
Windows Boot Manager (P1: Sandisk SSDF Plus 120GB)

Putting Win 10 SSD into other tray (set to UEFI) cause problems.

Sounds like I will have to be careful which tray I use for Win 10 (or else it gets befuddled)

- - - Updated - - -

ThrashZone said:

...fast start is disabled for starters.

Sounds like I have confused "fast boot" (BIOS option) with "fast start-up" (power option in Windows 10).

Disableing the latter have sorted out NAS mapped drive auto-connect on boot.
It seems to be working fine now.
Thank you!

Hi,
No problem
Disabling fast start in win-10
Command prompt as admin and this string will disable that pretty easily too
powercfg -h off

thanks !
and just to confirm - NAS autoconnect still works fine, so "fast start" was definitely a problem.