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Old 07-16-2007, 10:44 PM   #1
Simon Bridge
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lvm and data migration

I have increasingly seen situations where a user has a default fedora installation (say FC6) and they decide to upgrade, and upgrade the HDD at the same time.


They now have their brand new default f7 installation, plug in the old drive and expect to be able to mount it's ext3 partitions and just copy their data over. This would seem a reasonable expectation... only the defaults they have trusted have made an LVM volume out of their single drive. They get an error:
mount: wrong fs type, bad option, bad superblock on /dev/sdb2,
       missing codepage or other error
The good ones do the right things... they check /etc/fstab and fdisk -l and discover the LVM thing they've never heard of.

This is the point we expect users to issue plaintiff cries... IMO, justified: they're not expecting this!

However: this does not happen. Instead they do the correct, non-luser, thing and google about LVM. They read the man page and find a huge wealth of information.
All of it technical.

There is confusion because their old and new volumes have the same label.

Under a calm guidance, and since these are clearly not the run-of-the-will user, things get resolved. But I would have thought it would be simpler than this - handled at a higher level.

I can even sort-of see how... where a new volume (with an older datestamp) is introduced, which has the same VG name (i.e. VolGroup01) as an existing one, it seems this could well be a previous installation and could be common enough an occurrance to be anticipated.

In short: surely there is a standard tool for dealing with this?

I haven,t found one... but I am a simple soul.
I don't have a fedora install here to experiment with either. It isn't something I have had to deal with but for others: I haven't used a default install since RH9. I normally advise (and use) a custom scheme without LVM and a separate home partition for fedora.

Instead there is the old vgscan followed by vgchange -a y ... which is not all that worse than the regular mount command, just unexpected.

Can anybody shed light on this?

The purpose of this thread is part rant (so you good folks can tell me how silly I'm being) and part "collecting information" so a group of users who have been identified actually using the search functions will have some place to land.

No, I don't think this is bad enough to call a "bug" (in implementation) but if I get much more of these I'll reconsider.
Old 07-16-2007, 10:59 PM   #2
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The lvm problem has been around since at least FC4. Between the headaches like this and the fact that if it does crash it is a royal PITA I avoid LVM like the plague. It may take a few minutes to reinstall now with just straight ext3 (or whatever) but when somewhere down the road something pops up, you will be paid back with interest.

There is almost nothing that LVM does that you cannot do without it. If you want to add space to your home directory just put the mount point of the new drive(or partition) in your home directory. You can shrink and expand ext3 partitions too.

Yep, I got burned bad by LVM back in the FC4 days.

Old 07-17-2007, 01:34 AM   #3
Simon Bridge
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... I can see the advantage to totally new users having LVM on small systems. But not a big one. I do think that if LVM is the default, it should include some user education as well... better would be if anaconda offered three options: autopartition with LVM, autopartition without, and custom partition. The sidebar in anaconda can explain the pro's and cons. It is not a lot of text.

But this is besides the point: this is known since FC4 and there is nothing to ease the way?

A graphical tool for LVM is also beside the point. This is a very specific situation with an easily spotted condition (VG names are the same). Wouldn't it be nice to get a popup dialog telling you: "There are two volumes with the same name, one is the default for this system and takes precedence. What would you like to do with the other one?" with a list of options... mount as a separate volume, merge the volumes, extract data... you know.

Something like that will not be able to handle any other situation but a warning that VGs have the same name has got to be useful.

Hmmm... I'd also like opinions as to if these ideas are good enough to bring to a maintainers attention. Perhaps more refined?

As I say, I'd produce code but have not access to a fedora install or spare drives right now.
Old 07-17-2007, 01:48 AM   #4
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Lots of people have filed bug reports on bugzilla going back to FC4. Basically they reply that it would be too dangerous to let loose such a tool( or some other BS answer). Like gparted, etc, is not dangerous enough. Most of the people I have talked to would like to see LVM switched to an option(like raid) but apparently the powers that be want it as standard. Nobody I have talked to really understands why, just that there is no give on this point.


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