Here’s another silly one for you. What do you do if the latest release of your OS of choice ships with ZFS, but you don’t have space in your laptop for a second disk? …Answer:- Reach for the velcro.
This Sony Vaio has a Centrino Core-2 p8600 processor, so it’s not going to break any speed records, but it works well enough for day to day use. Courtesy of the Buffalo 500GB SSD taped to the lid, it now sports 1TB of disk space (500GB mirrored), which is probably well in excess of what the designers originally envisaged.
This is one of those little “because I can” projects which I don’t necessarily recommend to anyone else, but at the same time, the lightness of an SSD compared to a normal hard-disk (even a 2.5″ one) means this is now an eminently practical solution if your old laptop happens to be running out of space (I do move the laptop around the house to work in different rooms at different times, but it generally doesn’t travel much further afield than a deck-chair out on the veranda).
So, will it mirror? Heck yes!
Should I mirror?
No, probably not. It’s much more sensible to use a periodic ZFS send/receive job to back up your work to an existing server, that way you don’t need to worry about the extra drain on your battery and you still have your work if your laptop is stolen or knocked off the deck of your yacht, mid-ocean (what, you mean that’s never happened to you?).
One other consideration when thinking about installing Ubuntu on ZFS — currently (as of 21.04) Ubuntu will not allow you to edit the size of the disk partitions; you must accept their optimized defaults. Unfortunately , those defaults include a /boot partition which is much too small (typically 2GB). It will work fine for a couple of months, but with every apt update, the system will automatically add a snapshot of the boot partition. When the upgrade includes a kernel update, this means that tens, or even hundreds of megabytes of storage can be used. Even when you set the system defaults to compress the kernels using “xz”, it doesn’t take too many updates before you start getting “not enough free space” messages from apt and it will refuse to continue with the update. This is not something a novice user can easily recover from (hint: deleting files on a ZFS partition doesn’t always return that free space to the system — it all depends on whether it is still being held by a snapshot).