How to restore data from HDD

The data is not encrypted ... basically, the RAID controller writes RAID configuration data to beginning of the drive, where most OS's and programs will look for the partition table - they obviously aren't going to find the partition table and will find the RAID configuration data instead, which it can't read and doesn't know what to do with.

You MUST use hardware or software that supports your RAID controller - that knows how to read its configuration data.

Which RAID controller do you have?

"I need a system of plug and play on any PC so that I can recover data easily, just plug a drive to another PC as a slave drive and copy data from it"

This is not a sound backup strategy.  You need to keep backups in a way that the data can be restored to another (or the same) server/system in the event of failure.  If you insist on having it work this way, then you MUST get rid of any kind of RAID solution you might be using and simply use onboard SATA/ATA for storage, but again, this is not how you should be preparing for disaster.

Thank's for Your answer

I don't know which controler is inside this T110 II, I just change the settings in BIOS to raid and use like that.
 I will try to do something to about finding that controler type and try to get data.

About backup. I know it's not a great solution but it's the only one a customer will pay for. They had several IBM server that work great, even on system failure we make it working in few minutes. all we need is to take the SQL data and install SQL on any other machine and software works. They want that here to and we couldn't make it work. They have 15 (5 of these are DELL T110 II servers, other's are IBM) locations and only on one OS failed to boot and we could not extract data that's important to them. Raid is here because of hard drive failure. One will always die before two and that's why we go for raid.

That's why I need RAID and need plug and play. You can't sell someone another server of same type just to sit in corner and do nothing, just in case the master one fails because here in Bosnia people don't have or don't want to spend a lot of money on IT equipment. But in case of failure they want a quick solution to bring it back to working state while the server is being repaired.

Hope You understand why I need this system like this. The external HDD is here only because of fire some other disaster to take the data quickly with you and get out of there.

"I know it's not a great solution but it's the only one a customer will pay for."

You will need to turn off RAID in the BIOS and use an OS-managed RAID.  Nearly all RAID controllers write metadata to the beginning of the drive, making it impossible for a "regular" controller to read it.  It is not a form of vendor lockout, it is simple hardware implementation and management.

If all they need is the SQL data, why not back it up regularly to another machine?  If there are multiple machines, have them do a round-robin or double-round-robin backup to the other machines.

Your external HDD would also be a better choice if you already have it in place.  Sure it may be only for disasters, but why not for your more common local failures?  Or spend $90 on another external HDD that they can store the other backups.

Your customer needs to have their expectations set straight.  You might occasionally find a solution offering both RAID protection and universal portability, BUT that will be the exception to the norm and not the norm on RAID controllers.