How do I build a macbook air as a standby machine ?

Question

I have a 2010 13" dual core Macbook Air I want to build & maintain as a standby quick swap out machine in case my MBP crashes at the wrong time & is unrecoverable.
Assuming my external storage remains operable after the crash what do I need to consider in building the MBA as a standby machine to ensure a quick swap out with minimal data loss? I'm not looking to mirror the main machine's drive.
many thanks

Answer 1

you dont want to mirror the HD from the Pro on an external?
      Thats exactly what you DO need to do.
~~~~~~"in case my MBP crashes at the wrong time & is unrecoverable"
The working premise of any pro on any computer is to always always assume your notebook or desktop is going to crash and burn anytime all the time.
Why would your external storage NOT be operational after your machine crashes (if and when) ?
This is why its all about redundancy in multiples externally.  2 copies is 1, and 1 is none, and data ON the computer never counts in this scheme.
If you only have a single external backup or data archive, this is always a disaster in waiting, a single-point failure and tragedy-trap
As for your "fast recovery from a crash"
Nothing exists faster than a HD clone to boot from for ultra fast recovery from an internal HD or SSD crash.
see all details:
Methodology to protect your data. Backups vs. Archives. Long-term data protection
Peace
There are only two kinds of hard drives, those that have failed, and those that will fail, regardless of quality of manufacture.
Never consider any computer a data storage device at any time under any circumstance, rather a data creation, sending, and manipulation device. Anyone who thinks data is safe on any computer, even copied upon multiple partitions is making a mistake that will, without fail, strike.
Four words: "compartmentalized autonomous redundancy of data" or C.A.R.D. What this means regarding your data is
“centralize it, isolate it, and multiply it”.
This easy acronym to remember about how to approach your data is a great first approach to keep in mind.
Compartmentalized: separating out your data from your system files, centralizing all static and active files into a location or two to make backups, and archived data easier to update and locate. Centralizing your data collection is the primary hazard to overcome for what usually is the case of data that is scattered everywhere throughout your internal hard drive.
Autonomous: Isolation of data from changes, theft, decentralizing data to safes, fire boxes, offsite and online locations. Importantly ‘freezing’ data onto independent storage media for protection and from alterations, such as DVDs, hard drives, and online encrypted files, or .DMG created files of static data collections.
Redundancy: making copies of all autonomous isolated data such that data is decentralized not only in place and in media storage type (DVD, HD, online) for safety and protection as a failsafe, but each aspect of that failsafe has at the very least two redundant copies.
Data: all files made, saved, created, modified or working on. Important pictures, documents, videos, PDF, financial, personal. Any data large or small which you would not dare lose, which is private, important, hard or impossible to recreate, or most importantly, would take tremendous time to regenerate. Essentially anything important to you, your company, your loved ones (will, medical records, financial information, etc.), friends or otherwise.