Re: Ideas for btrfs-convert fix(or rework)

[Austin S Hemmelgarn]

On 2015-11-12 09:09, Roman Mamedov wrote:

On Thu, 12 Nov 2015 08:27:49 -0500
Austin S Hemmelgarn <ahferro...@gmail.com> wrote:

know of (Arch and Gentoo), because the very fact that you installed a
system with either one means that you are fully capable of backing up
your data, and reprovisioning the system using BTRFS instead of whatever
filesystem you are already using

Uhm, what?... How does the fact that I use one particular distro or another,
reflect on my ability to (easily) back up and restore my 10 TB storage array?
"You should maintain backups anyway so you could easily restore" -- yeah I do,
and they are in a remote location over a relatively slow link.

I did not mean to imply that you had the ability to do it quickly, just the ability to do it. I specifically stated 'very little' instead of 'none' to account for cases like yours. However, the statement is still accurate because Arch and Gentoo both have very low-level user involvement in the install process (no GUI, user manually provisions the storage and handles installing the base system). If you are capable of installing such a system (and as such, capable of correctly using stuff like parted or fdisk without breaking anything), you are absolutely capable of reprovisioning such a system (how long that would take is a completely different matter).

I chose Ext4 instead of the other options which seemed more attractive
(primarily XFS, but also JFS) for this array back when creating it a long time
ago, when Btrfs was still in its much earlier days than now, **SPECIFICALLY**
with the intent to use btrfs-convert "as soon as Btrfs somewhat matures". So
as time went, it did, I acted on this plan, and everything went just perfectly.

And you got somewhat lucky in that case (and actually did proper research, sadly most people don't seem to do anywhere near enough research when it comes to stuff like this). Doing an in-place conversion of a filesystem (or an OS, or anything else for that matter) is _always_ going to be inherently more risk than just properly reprovisioning (take a look at the absolute insanity that is the 'free' Windows 10 upgrade for an example of this on the OS side). Admittedly, compared to other software that does this (the only other program that I know of to do this is fstransform), btrfs-convert is relatively safe, but it is not possible for it to be any safer than just reprovisioning.

Why are people so quick to project "If I don't need this, nobody likely does".
Btrfs-convert is an amazing feature and it will be extremely sad if it ever
goes away.

And as time goes on, it will be used less and less, and it's _always_ going to be something that 99% of users who actually use it (if you're doing any kind of RAID, it makes more sense from a data safety perspective to just reprovision so you can use BTRFS's native raid functionality) run exactly once per filesystem per system (once you've converted existing systems, you don't need it unless you were using dump for backups). I'm not arguing that it should just go away, I'm trying to argue that it shouldn't be a development priority if it works correctly.

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