F32->F33: Upgrade or reinstall?

[Patrick O'Callaghan]

I'd normally upgrade, but my /dev/sda uses LVM to handle root, /home
etc. and from what I read this cannot be converted directly to BTRFS,
which I'm interested in using.

What would be the best way to approach this?:

1) Do a system upgrade and then convert to BTRFS by backing everything
up and restoring it (I'd need guidance on how to do this).

2) Do a complete system install and then restore from backups.

I'm guessing that (2) is the simplest answer, but I'd appreciate any
comments, especially from people who have actually done either of
these.

poc

[Sam Varshavchik]

Patrick O'Callaghan writes:

>  I'd normally upgrade, but my /dev/sda uses LVM to handle root,
> /home
>  etc. and from what I read this cannot be converted directly to BTRFS,
>  which I'm interested in using.
>
>  What would be the best way to approach this?:
>
>  1) Do a system upgrade and then convert to BTRFS by backing everything
>  up and restoring it (I'd need guidance on how to do this).
>
>  2) Do a complete system install and then restore from backups.
>
>  I'm guessing that (2) is the simplest answer, but I'd appreciate any
>  comments, especially from people who have actually done either of
>  these. 
If you're set on this kind of a disruption, a clean install, followed by  
restoring your home directory from backups, will be more reliable.  
Attempting to do /full/ reinstall of the /entire/ system from backups is a  
much more complicated affair. Your backup/restore method must correctly not  
just reinstall files and set their ownership and permissions, but also all  
other extended attributes, specifically selinux contexts. I'm not aware of  
anything in Fedora that uses other extended attributes for something, but  
there may be.

This is less of an issue when restoring just your home directory from  
backups.

[Patrick O'Callaghan]

On Mon, 2020-11-02 at 08:19 -0500, Sam Varshavchik wrote:
>  Patrick O'Callaghan writes:
>  
>  > I'd normally upgrade, but my /dev/sda uses LVM to handle root, /home
>  > etc. and from what I read this cannot be converted directly to BTRFS,
>  > which I'm interested in using.
>  > 
>  > What would be the best way to approach this?:
>  > 
>  > 1) Do a system upgrade and then convert to BTRFS by backing everything
>  > up and restoring it (I'd need guidance on how to do this).
>  > 
>  > 2) Do a complete system install and then restore from backups.
>  > 
>  > I'm guessing that (2) is the simplest answer, but I'd appreciate any
>  > comments, especially from people who have actually done either of
>  > these.
>  
>  If you're set on this kind of a disruption, a clean install, followed by  
>  restoring your home directory from backups, will be more reliable.  
>  Attempting to do /full/ reinstall of the /entire/ system from backups is a  
>  much more complicated affair. Your backup/restore method must correctly not  
>  just reinstall files and set their ownership and permissions, but also all  
>  other extended attributes, specifically selinux contexts. I'm not aware of  
>  anything in Fedora that uses other extended attributes for something, but  
>  there may be.
>  
>  This is less of an issue when restoring just your home directory from  
>  backups. 
That makes sense, thanks. I will also need to restore some things in
/etc of course, but that can be done manually.

poc

[Samuel Sieb]

On 11/2/20 4:45 AM, Patrick O'Callaghan wrote:
>  I'd normally upgrade, but my /dev/sda uses LVM to handle root,
> /home
>  etc. and from what I read this cannot be converted directly to BTRFS,
>  which I'm interested in using. 
https://fedoraproject.org/wiki/Btrfs

[Chris Murphy]

On Mon, Nov 2, 2020 at 5:45 AM Patrick O'Callaghan
<pocallaghan(a)gmail.com&gt; wrote:
>  I'd normally upgrade, but my /dev/sda uses LVM to handle root, /home
>  etc. and from what I read this cannot be converted directly to BTRFS,
>  which I'm interested in using. 
ext4 can be converted to Btrfs but I can't strongly recommend it
because you're not going to get the same layout as a default
installation. The conversion won't remove LVM, and it won't add the
subvolume layout we're using where "home" and "root" subvolumes
are
assigned to /home and / mountpoints respectively.

>  What would be the best way to approach this?:
>
>  1) Do a system upgrade and then convert to BTRFS by backing everything
>  up and restoring it (I'd need guidance on how to do this).
>
>  2) Do a complete system install and then restore from backups.
>
>  I'm guessing that (2) is the simplest answer, but I'd appreciate any
>  comments, especially from people who have actually done either of
>  these. 
Top choice:
Backup /home. Optionally /etc. And hand it over to the installer for
complete wipe and clean install. From scratch setup. And after going
through initial setup, restore /home (specifically restore the
contents of ~/ for each user). Probably the most straightforward.

Second choice:
Esoteric but a rather neat trick, is btrfs conversion, snapshot root
and home. And use Btrfs send/receive to populate a new Btrfs file
system with those snapshots. The conversion to Btrfs is merely a means
to being able to use send/receive to replicate them. You get to keep
your customizations without a clean install, but you do get the
subvolume layout of a clean install. It is a bit partition-ninja. And
there are post steps like all the bootloader stuff. It really depends
on how comfortable you are with a rather low level process of
migrating the data, almost inevitably messing it up, and working
through the screwups. I've done quite a few of these and manage to
screw it up somehow, and have to backtrack but I also don't panic
easily, not least of which is a bunch of backups. So no matter how
badly I mess it up I know I'm not losing things I care about.

-- 
Chris Murphy

[Christopher Ross]

On 03/11/2020 07:13, Chris Murphy wrote:
>  On Mon, Nov 2, 2020 at 5:45 AM Patrick O'Callaghan
>  <pocallaghan(a)gmail.com&gt;  wrote:
> > I'd normally upgrade, but my /dev/sda uses LVM to handle root, /home
> > etc. and from what I read this cannot be converted directly to BTRFS,
> > which I'm interested in using.
>  ext4 can be converted to Btrfs but I can't strongly recommend it
>  because you're not going to get the same layout as a default
>  installation. The conversion won't remove LVM, and it won't add the
>  subvolume layout we're using where "home" and "root" subvolumes
> are
>  assigned to /home and / mountpoints respectively.
>
> > What would be the best way to approach this?: 
[snip]
> > 2) Do a complete system install and then restore from backups.
> >
> > I'm guessing that (2) is the simplest answer, but I'd appreciate any
> > comments, especially from people who have actually done either of
> > these.
>  Top choice:
>  Backup /home. Optionally /etc. And hand it over to the installer for
>  complete wipe and clean install. From scratch setup. And after going
>  through initial setup, restore /home (specifically restore the
>  contents of ~/ for each user). Probably the most straightforward.
>  
Is this the best advice for complicated setups too? My main computer has 
been upgraded again and again since about Fedora 18, with parts being 
changed out as and when. When new disks are added the old ones remain 
until they die; where I have multiple disks of the same size I RAID them 
for performance. My current disk setup looks like this:

root@snoopy 09:22:35 ~ # lsblk --merge
           NAME               MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
           sda                  8:0    0 111.8G  0 disk
           ├─sda1               8:1    0   500M  0 part  /boot
       ┌┈▶ └─sda2               8:2    0 111.3G  0 part
       ┆   sdb                  8:16   0 111.8G  0 disk
       ┆   ├─sdb1               8:17   0    64G  0 part  [SWAP]
       └┬▶ └─sdb2               8:18   0  47.8G  0 part
        └┈┈fedora_snoopy-root 253:0    0 159.1G  0 lvm   /
           sdc                  8:32   1  14.6T  0 disk
           └─sdc1               8:33   1  14.6T  0 part  /backup
           sdd                  8:48   0 931.5G  0 disk
       ┌┈▶ └─sdd1               8:49   0 931.5G  0 part
       ┆   sde                  8:64   0 931.5G  0 disk
       ├┈▶ └─sde1               8:65   0 931.5G  0 part
       ┆   sdf                  8:80   1   3.7T  0 disk
    ┌┈▶┆   └─sdf1               8:81   1   3.7T  0 part
    ┆  ┆   sdg                  8:96   1   3.7T  0 disk
    └┬▶┆   └─sdg1               8:97   1   3.7T  0 part
┌┈▶ └┈┆┈┈┈md1                  9:1    0   7.3T  0 raid0
┆     ┆   sdh                  8:112  0 931.5G  0 disk
┆     ├┈▶ └─sdh1               8:113  0 931.5G  0 part
┆     ┆   sdi                  8:128  0 931.5G  0 disk
┆     └┬▶ └─sdi1               8:129  0 931.5G  0 part
└┬▶    └┈┈md0                  9:0    0   3.7T  0 raid0
  └┈┈┈┈┈┈┈┈vg_home-lv_home    253:1    0  10.9T  0 lvm   /home
           sr0                 11:0    1 496.7M  0 rom

If I do a clean install of Fedora 33 onto this will it cope? I am hoping 
that BTRFS / Anaconda will spot all those disks and make optimal use of 
them, better even than my manual arrangement. Is that a fair assumption, 
or would I be better just upgrading F32 -> F33 as previously?

Many thanks,
Chris R.

[Chris Murphy]

On Tue, Nov 3, 2020 at 2:25 AM Christopher Ross <fdra6390(a)tebibyte.org&gt; wrote:

>  Is this the best advice for complicated setups too? My main computer has
>  been upgraded again and again since about Fedora 18, with parts being
>  changed out as and when. When new disks are added the old ones remain
>  until they die; where I have multiple disks of the same size I RAID them
>  for performance. 
Offhand I don't see a reason to change strategies. Over that time
frame there are likely ext4 and XFS features that you don't have
access to without a reformat. Offhand, checksummed journal and
metadata (in both file systems). And reflink copies are now supported
on XFS since about 1 year. Btrfs is a bit different in that it takes
advantage of feature flags which can be set on existing file systems
rather than a reformat [1].

My current disk setup looks like this:
>  root@snoopy 09:22:35 ~ # lsblk --merge
>             NAME               MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
>             sda                  8:0    0 111.8G  0 disk
>             ├─sda1               8:1    0   500M  0 part  /boot
>         ┌┈▶ └─sda2               8:2    0 111.3G  0 part
>         ┆   sdb                  8:16   0 111.8G  0 disk
>         ┆   ├─sdb1               8:17   0    64G  0 part  [SWAP]
>         └┬▶ └─sdb2               8:18   0  47.8G  0 part
>          └┈┈fedora_snoopy-root 253:0    0 159.1G  0 lvm   /
>             sdc                  8:32   1  14.6T  0 disk
>             └─sdc1               8:33   1  14.6T  0 part  /backup
>             sdd                  8:48   0 931.5G  0 disk
>         ┌┈▶ └─sdd1               8:49   0 931.5G  0 part
>         ┆   sde                  8:64   0 931.5G  0 disk
>         ├┈▶ └─sde1               8:65   0 931.5G  0 part
>         ┆   sdf                  8:80   1   3.7T  0 disk
>      ┌┈▶┆   └─sdf1               8:81   1   3.7T  0 part
>      ┆  ┆   sdg                  8:96   1   3.7T  0 disk
>      └┬▶┆   └─sdg1               8:97   1   3.7T  0 part
>  ┌┈▶ └┈┆┈┈┈md1                  9:1    0   7.3T  0 raid0
>  ┆     ┆   sdh                  8:112  0 931.5G  0 disk
>  ┆     ├┈▶ └─sdh1               8:113  0 931.5G  0 part
>  ┆     ┆   sdi                  8:128  0 931.5G  0 disk
>  ┆     └┬▶ └─sdi1               8:129  0 931.5G  0 part
>  └┬▶    └┈┈md0                  9:0    0   3.7T  0 raid0
>    └┈┈┈┈┈┈┈┈vg_home-lv_home    253:1    0  10.9T  0 lvm   /home
>             sr0                 11:0    1 496.7M  0 rom
>
>  If I do a clean install of Fedora 33 onto this will it cope? I am hoping
>  that BTRFS / Anaconda will spot all those disks and make optimal use of
>  them, better even than my manual arrangement. Is that a fair assumption,
>  or would I be better just upgrading F32 -> F33 as previously? 
That's pretty complex. I'd say just keep it until you've got a good
reason to change it. It's valid to put Btrfs on these device mapper
layers. It might be easiest to do this in the Advanced-Custom
partitioning UI so you can be very explicit about what you want.
Automatic partitioning is intended for the more simple case of one or
maybe two drives.

In the somewhat common case of two drives: NVMe and one large HDD, if
you hand over both drives to the installer, Fedora 32 and older makes
the largest partition on both drives PV's and adds them to one VG. And
on Fedora 33 now using Btrfs it creates one big btrfs out of those
partitions, in a functionally similar "concatenate" arrangement [2]
This is probably suboptimal by most estimations. I think most people
would probably want all the boot, system related things, and
applications on the NVMe drive, and /home on the HDD. Automatic
partitioning doesn't have a way to anticipate these things.

It's also valid to mix and match if you want. You can repurpose your
existing root LV with a new clean install that uses Btrfs just for
system root; and reuse your ext4 on LVM "home" LV assigned to /home
mountpoint without reformatting. If you want a Btrfs /home at some
point, you've got the option to either convert it; or do the backup,
mkfs, restore dance.

Btrfs does not offer different raid levels for subvolumes. The
redundancy profile is set separate on metadata block groups and data
block groups, for that entire file system. So if you want raid0 for
system stuff and raid1 for user files, those are still separate file
systems.



[1] Three things are mkfs only options: (--csum) checksum algorithm is
crc32c by default; (--nodesize) the metadata block size is 16KiB by
default; (--mixed) mixed block groups instead of separate metadata and
data block groups which is the default, tends to be used for small
devices under 5GiB, like USB sticks. Everything else can be changed
after mkfs time.

[2] The small difference is that the Btrfs mkfs default for multiple
devices uses raid1 for the metadata block group. Metadata in the Btrfs
context means the file system itself, such as the various trees that
include things like file inodes and the references to where the data
itself is located. To say "metadata profile is raid1" means two copies
of the file system, meaning one device can file and the file system
itself is OK. Since there's only one copy of data, anything on a
failed drive is lost, so this is not likely a bootable system. But
files on surviving drives are OK.

-- 
Chris Murphy

[Patrick O'Callaghan]

On Tue, 2020-11-03 at 00:13 -0700, Chris Murphy wrote:
>  On Mon, Nov 2, 2020 at 5:45 AM Patrick O'Callaghan
>  <pocallaghan(a)gmail.com&gt; wrote:
>  > I'd normally upgrade, but my /dev/sda uses LVM to handle root, /home
>  > etc. and from what I read this cannot be converted directly to BTRFS,
>  > which I'm interested in using.
>  
>  ext4 can be converted to Btrfs but I can't strongly recommend it
>  because you're not going to get the same layout as a default
>  installation. The conversion won't remove LVM, and it won't add the
>  subvolume layout we're using where "home" and "root" subvolumes
> are
>  assigned to /home and / mountpoints respectively. 
OK.

>  > What would be the best way to approach this?:
>  > 
>  > 1) Do a system upgrade and then convert to BTRFS by backing everything
>  > up and restoring it (I'd need guidance on how to do this).
>  > 
>  > 2) Do a complete system install and then restore from backups.
>  > 
>  > I'm guessing that (2) is the simplest answer, but I'd appreciate any
>  > comments, especially from people who have actually done either of
>  > these.
>  
>  Top choice:
>  Backup /home. Optionally /etc. And hand it over to the installer for
>  complete wipe and clean install. From scratch setup. And after going
>  through initial setup, restore /home (specifically restore the
>  contents of ~/ for each user). Probably the most straightforward. 
Yes, that looks like what I'll go for.

>  Second choice:
>  Esoteric but a rather neat trick, is btrfs conversion, snapshot root
>  and home. And use Btrfs send/receive to populate a new Btrfs file
>  system with those snapshots. The conversion to Btrfs is merely a means
>  to being able to use send/receive to replicate them. You get to keep
>  your customizations without a clean install, but you do get the
>  subvolume layout of a clean install. It is a bit partition-ninja. And
>  there are post steps like all the bootloader stuff. It really depends
>  on how comfortable you are with a rather low level process of
>  migrating the data, almost inevitably messing it up, and working
>  through the screwups. I've done quite a few of these and manage to
>  screw it up somehow, and have to backtrack but I also don't panic
>  easily, not least of which is a bunch of backups. So no matter how
>  badly I mess it up I know I'm not losing things I care about. 
Here be dragons :-) No thanks, I had enough trouble getting my head
around LVM (one reason I'm keen to move to BTRFS).

poc