[linux-lvm] vgscan not returning UPDATE
Ali Zaidi
smaliz at ureach.com
Fri Sep 20 16:50:29 UTC 2002
I seem to have LVM working for me now.
This is just so some of you guys can tell me if i have done something horribly
wrong.
As vgscan was never returning, i did a strace on it and found out that it was
getting stuck at a read call for /dev/nb0.
As i would only be using /dev/hd devices for LVM, i figured if i can comment
out references to "nb" from the LVM source, that might do the trick.
I ended up commenting out two lines from tools/lib/lvm_dir_cache.c and one line
from tools/lib/lvm_check_partitioned_dev.c.
After recompiling, vgscan now returns and i was also able to run pvcreate and
vgcreate successfully.
As i understand, if i am not going to be using Network Block devices under LVM,
i should be fine with the above arrangement.
Ali
---- On Thu, 19 Sep 2002, James Hawtin (oolon at ankh.org) wrote:
>
>
> On Thu, 19 Sep 2002, Ali Zaidi wrote:
>
> > Hi:
> > I am a novice with LVM but after going through the man pages and howtos i
was
> > unable to find a solution to my problem. I am hoping one of you might find
some
> > time to point me in the right direction.
> >
> > I am trying to setup LVM on a RH box. I run vgscan before i can create the
> > volumes but it never returns. Same thing happens with lvmdiskscan and
pvscan.
> > Here is a -v and -d output of vgscan
>
> Ok and now to try to answer your problem....
>
> Did you do a pvcreate?
>
> did the disk have existing data on it?
>
> Try dd to write /dev/zero to the first bit of the partitions you want to
> put into lvm. then do you vgscan which should then return with an error
> saying it found nothing.... you can then use pvcreate on them
>
> Of course your LAME disk layout could be confusing lvm in which case as a
> work arround just have one lvm partion and use lvm to allocate the disk,
> which is what you should be doing in the first place!
>
>
> ------
>
> And now a few quick questions and answers....
>
> Q: I can allocate my disk better than LVM!
>
> A: No you cannot! or rather you can allocate your disk when you
> first get the machine to produce nice continuous partions. YOU CAN DO THIS
> WITH LVM. If you have a brand new volume group and just add partions to
> it they will be continuous with LVM as well.... Don't trust LVM.. you can
> do a pvdisplay to show you this fact!
>
> A2: Sure, but what happens if you want to remove 2 partions, that are not
> next door to each other, and them make the one big partion... with fdisk
> its a dd nigtmare... with LVM its easy.
>
> Q: but how can I move my stuff onto another disk... I use DD!
>
> A: SO? There is nothing special about lvm devices apart from the fact they
> make things easer for you... You want to work that way, make your new
> device using LVM or fdisk and do your dd! But you could save yourself time
> by using pvmove!
>
> Q: LVM adds a level of indirection to my disk.. surely its better to use
> the real disk
> A: Theoritically yes... but the translation to where on the disk is a
> calculation done on your computer not on the disk the slowest part of the
> operation is pulling stuff from your disk! Think about is a software raid
> faster or slower? Its faster cos the slow part was the disk and now there
> is more than one disk!
>
> Q: I like to micromanage my disk...
> A: You can do that with LVM if you like or you can let LVM do the best it
> can for you and use your bonus time to go down the pub.
>
>
> James
>
>
> _______________________________________________
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> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
>
>
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