On Tue, Dec 19, 2023 at 7:51 AM Philip Rhoades via users <
users@lists.fedoraproject.org> wrote:

> People,
>
> I have been using Fedora since Core 1 and still have the old HDs and I
> have kept using ext[234] FSs just for simplicity / consistency up to the
> current time (F39) - but now I want to experiment with btrfs and I was
> thinking I could go through the exercise of converting an old SATA boot
> drive where I am still using /dev/sdd5 (the old /home partition) as one
> of a few backup partitions / drives for current live data from my
> workstation and some small servers.
>
> At first I was thinking I could delete ext4 parts 1-4, replace them with
> a new btrfs partition and then maybe somehow use btrfs-convert to
> integrate the remaining ext4 part 5 into the new part 1?


I think the process would be to delete the disposable partitions, expand the
remaining partition to the full drive, and then convert.  The conversion
needs
extra space for BTRF metadata, but I think it preserves the existing data
blocks.
At work we copied data to a (large, striped) filesystem, processed it, and
then
moved the results to long-term storage, rinse and repeat.  We found that
drive
failure rates increased around end-of-warranty, so I worry about intensive
disk
activity on older drives pushing them to failure.


> . . but what I
> really want to do is create a new btrfs using the _whole_ of the disk -
> but somehow avoid having to spend a LONG time copying back about 4TB (to
> the 8TB drive) - the only way I could see that possibility working is to
> somehow do a recovery on the rest of the disk after the newly-created
> btrfs only takes up part of the beginning of the disk but leaves the old
> ext4 dirs and files recoverable somehow from near the beginning of the
> disk to just past halfway on the disk .
>

My reading of the btrfs-convert man page is that the ext4 data blocks are
preserved, so the main concern is to avoid having btrfs metadata fragmented
if the free space in the old ext4 partition is fragmented.   Filesystem
work better
when they have plenty of elbow room.

-- 
George N. White III
--
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