Bug#783089: debian-installer: Cannot rescue a system installed on a raid1 lvm
Le 2015-04-22 14:20, Lennart Sorensen a écrit :
On Wed, Apr 22, 2015 at 07:49:02AM +0200, Jean-Yves LENHOF wrote:
Because I prefer do it this way... lvm raid is more the traditionnal
unix way of doing it (AIX and HP-UX for sure)
Taste is personnal... There are advantages and inconvenients in all of
them (Linux/AIX/HP-UX/True64/Solaris/FreeBSD/whatever)
FOR AIX vs linux some examples :
some pro :
smitty is nicely implemented (there was linuxconf in the past days of
linux but not maintained anymore)
mksysb is something nice to use to restore a system or to install a
system with the same configuration...
alternate install is something interesting when upgrading from an OS
version to another one (using an alternate lvm mirror)
some con :
odm is something you should not touch without IBM advise, etc..
dependencies in packages are too hard and upgrading a package tend to
have everything upgrading...
But we are not here to speak about proprietary... but about Linux, so I
will not elaborate more on that.
That doesn't mean it is a good idea. Those two certainly qualify as
the most unpleasant unix systems I have ever had to work with.
Why it is very inflexible ? It found it quite flexible.
You can't easily add disks to the volume group in raid mode (as far as
I recall the documentation last I looked at it). There are certainly
restrictions on how to you expand volumes when lvm raid is in use.
I just add a disk on my test partition... Done a pvcreate on it, done a
vgextend on it without problem.
Done a lvextend on a logical partition... Resize my slashlv file system.
No problem at all. Did you remake some recent tests ? What is the
limitation you are speaking about ? The one I know is that you can't use
lvm raid1 in a cluster yet. (It's written in the RedHat Enterprise 7
Logical Volume Documentation)
Perhaps the md raid support is there from a longer time because raid1
support (which is different from mirror support) in the kernel (and in
lvm2 tools) came later... But things changes and I saw a lot of good
things coming in LVM like thin lvm support or cache lvm support. Read
redhat docs, such things are supported by RedHat since RedHat
Enterprise
6.4 or such.
Well certainly grub understands md raid, and it understands some lvm.
It might not understand lvm with raid. Following the grub development
mailing list for a number of years now, I can say I have never seen
anyone ask about it or even mention it. I think it is also the first
time I have seen it mentioned on any of the debian lists I follow.
You should have read my bug report about grub... There is at least one
another person than me that create the bug report ;-)
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=782591
http://savannah.gnu.org/bugs/?func=detailitem&item_id=44534
http://lists.gnu.org/archive/html/bug-grub/2015-04/msg00003.html
and you should probably read more carefully the list :
http://lists.gnu.org/archive/html/grub-devel/2014-08/msg00024.html
Certainly using lvm on top of md raid has worked for years for me and
the debian rescue knows how to deal with is, as does knoppix and lots
of other rescue systems. The lvm raid, no idea. When I looked at it
a few years ago it cretainly sounded like a bad option so I avoided it.
Some years ago you probably test the mirror type... which I agree is not
a so good solution.
I speak about the raid1 type which is different
raid1 is there since 2013 (there's no clear appareance of the first
commit related) :
https://git.fedorahosted.org/cgit/lvm2.git/tree/WHATS_NEW
For mirror, the mirroring is rebuilt at each reboot
For raid1, the mirroring isn't rebuilt at each reboot
I will see if I can provide a patch... because I think that discussion
is rubbish and code is better. I think it's just an option to add
somewhere to enable the built of this kernel module in an udeb.
For the debian-installer part (for this bug report here I speak about
rescuing) I will make another wishlist bug report (there will be more
impact because there will be some more device with rmeta in their name)
Please take the time to enable this module kernel in the udeb.
Regards,
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