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

[Duncan <1i5t5.duncan@cox.net>]

Qu Wenruo posted on Tue, 10 Nov 2015 17:18:02 +0800 as excerpted:

> Yes, some problem can be fixed by such balance, as after balance, data
> and metadata will be relocated to correct new chunks.
> 
> But there may be a lot of hidden bugs here.
> And we can't ignore such malfunction just because it's OK under some
> cases, or btrfs won't really become a production ready filesystem.

Very good point in general, but remember the context we're talking about 
here, btrfs-convert.

Convert is used once, if then, and a lot of generally considered stable 
filesystems get along perfectly fine without direct convert-from-ext* 
tools at all, telling people to either use their ext* as backups and 
restore/copy to their newly created filesystems of whatever new type, or 
backup the data they want to save from the old filesystem, then mkfs them 
directly to the new filesystem type, again, restoring/copying the backed 
up data back from the backups.

And after all, people using anything /other/ than ext* are going to have 
to do that anyway, unless even /more/ work is invested to deal with all 
the /other/ filesystems... all for something that's optionally used once 
and must work well if used, then forgotten about.

So an ext* specific convert tool, while definitely nice to have, remains 
entirely optional, and as such, unlike more critical actual filesystem 
features that will continue to be used as long as the filesystem exists, 
isn't really critical to btrfs becoming a production ready filesystem at 
all, because at some point, if it's still buggy it can simply be thrown 
away.

So a buggy convert tool, being optional, doesn't really affect the 
production readiness of the filesystem as a whole, at all.

Meanwhile, people really considering production readiness, at least in 
the enterprise setting, tend to be a pretty conservative bunch, and I'd 
argue that conservative admins will be unlikely to really trust such a 
conversion tool in any case, preferring to restore from existing 
backups.  I certainly know that /I'd/ have my doubts about trusting my 
data to a convert tool, and would /much/ rather do the copy over to the 
new filesystems thing, since at least that way, if anything goes wrong I 
know I still have the unchanged old copy that was perfectly fine to use 
the day/hour before still there and just as perfectly fine to use again.  
That's not something I'd be confident saying about the if-anything-goes-
wrong behavior of a convert-in-place tool!

So again, yes, convert is nice to have even if I'd never fully trust them 
myself, but it really doesn't affect the production readiness of the 
filesystem itself.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman