replace a ufs install by a zfs one

hern42 · Thursday at 5:42 AM

hi all,
i recently learned abour sylve and was eager to try it. stop me if i'm wrong but it looks like proxmox, which was also something i wanted to try on one server.
so i did install sylve and unfortunately it works only on zfs pools.

so my system is a laptop with a ssd hd with the system and a spinning one for data, the spinning one is on zfs but i fucked up my install of the system when upgrading to 15.1 and it's on ufs. i'd like to redo the install but without the hassle of all the backup and reconfig.
my idea was to repartition the ssd in two, install 15.1 on a zpool, tranfer all necessary files from the other partition, then reformat it on zfs, i'd have then two "data" partition (the sfs on the large hd and the half of the ssd) and one "system" one on half the ssd.

first off, is it a good idea?
second, would that work?

thanks for your help, as always,
yrs trly,
a-

LibreQuest · Thursday at 6:21 AM

I vote you try it and report back on your progress. I would personally go with backing up data and configs files. But, that's not as interesting as your proposal.

Maturin · Thursday at 8:23 AM

hern42 said:
i'd like to redo the install but without the hassle of all the backup and reconfig.

Always remember Murphy's law: 'Anything that can go wrong will go wrong.'

It's always:
1. Always ensure you have your data and config files backupped, maybe the whole drive cloned, to a safe place (additional drive being untouched by this stunt.)
2. Maybe erase the according drive first, but then change/create a new partition scheme/FS.
3. Copy your data from BU to it.

What you also can do, is to replace the drive by an empty (new) one, create your wanted partition scheme/FS on it, and copy the data from the former drive to it.
But never ever do any modifications of the partitions or filesystems on storage drives without a BU.

Doing such things may work without data loss, but even for things doable technically without data loss in theory there is a real chance such can result in data loss. (Murphy)

So, it was bad advice to give green light for any modifications on storage drives without having made a BU first.

If you don't have an empty additional drive you can get a 300 G external USB HDD for 20 €, or (IMO better) an "internal" 500 G HDD for 20 € plus a SATA to USB adapter for 10 €, (there are also M.2 to USB adapters.) Such to have is very recommendable anyway (e.g. for exactly such stunts.)
NO flashdrives/USB sticks/sdcards! Those are not reliable enough for being trusted BU media.

If you are too cheap to get an additional drive, or just too lazy to do such a stunt without BUs, you are completely on your own. You may try it. It may work. It may end in desaster.
It's neither FreeBSD's, nor the FS's, nor antyhing or anybody else's fault, when you got data loss, and don't have a BU.
And I hate to say, 'I told you so.'

Anyway it's 100% your own responsibility.

No excuses. No exceptions. Backups. Always.

hern42 · Thursday at 8:15 PM

Maturin said:
Always remember Murphy's law: 'Anything that can go wrong will go wrong.'

It's always:
1. Always ensure you have your data and config files backupped, maybe the whole drive cloned, to a safe place (additional drive being untouched by this stunt.)
2. Maybe erase the according drive first, but then change/create a new partition scheme/FS.
3. Copy your data from BU to it.

What you also can do, is to replace the drive by an empty (new) one, create your wanted partition scheme/FS on it, and copy the data from the former drive to it.
But never ever do any modifications of the partitions or filesystems on storage drives without a BU.

Doing such things may work without data loss, but even for things doable technically without data loss in theory there is a real chance such can result in data loss. (Murphy)

So, it was bad advice to give green light for any modifications on storage drives without having made a BU first.

If you don't have an empty additional drive you can get a 300 G external USB HDD for 20 €, or (IMO better) an "internal" 500 G HDD for 20 € plus a SATA to USB adapter for 10 €, (there are also M.2 to USB adapters.) Such to have is very recommendable anyway (e.g. for exactly such stunts.)
NO flashdrives/USB sticks/sdcards! Those are not reliable enough for being trusted BU media.

If you are too cheap to get an additional drive, or just too lazy to do such a stunt without BUs, you are completely on your own. You may try it. It may work. It may end in desaster.
It's neither FreeBSD's, nor the FS's, nor antyhing or anybody else's fault, when you got data loss, and don't have a BU.
And I hate to say, 'I told you so.'

Anyway it's 100% your own responsibility.
No excuses. No exceptions. Backups. Always.

oh my! yes! absolutely. i do have a full back of my /home
and of the data on the ssd hd. several times.

but, technically, aside from the überubiquitous murphy, this could work?
this is gonna be fun, as in "losing is fun" from dwarf fortress

thanks for the heads up about back up, one is never told enough to back shit up. never.

Maturin · 2026-09-04T05:58:46+0100

hern42 said:
but, technically, aside from the überubiquitous murphy, this could work?

As LibreQuest already said, try it - it's the best way to find out and learn.
As long as you do have backups, nothing can happen, so who's stopping you?

By your OP I am not 100% sure what exactly you're trying to do. But as far as I think I got it, you want to move your data from one internal drive (SSD) to the other (HDD), and after repartitioning and reinstalling 15.1 with ZFS on the SSD (probaly even a NVME, like I have in my laptop: one NVME containing the system + a HDD to store data ["porn" I sloppy say short for "movies, music, books, PDFs,..."]) you want to move /home and config files back to the system's SSD.
Sure, I don't see not why this shall not work. Technically you are doing an internal backup and restore from it.
All you need to look out for is to not confuse the drives, so accidently deleting your data on the HDD. Such fatfingering was one of the things Murphy's law is about. So better have another redundancy copy of those.
And above all you need to see your configs suit the new situation. Particulary I mean: Watch out to not just overwrite your new /etc/rc.conf with our old one, since you change from UFS to ZFS, so you need

Code:

zfs_enable="YES"

in your /etc/rc.conf, which is missing in your UFS version.

Better edit your new /etc/rc.conf you got by the new installation manually while having the old one open in another window.