[linux-lvm] snapshots not stable with 2.3.99pre2

[linux-lvm] snapshots not stable with 2.3.99pre2

[Jan Niehusmann]

While testing lvm with linux 2.3.99pre2 I had 2 crashes while trying out snapshots.
Without snapshots lvm seems to be stable.

Another problem is (probably) a missing check in lvextend: I tried to extend a
striped lv, and while I had enough space available, nearly all this space was on
one pv, so it was not possible to create a correctly striped volume with the 
extended size. But I didn't get the error message I expected: lvextend told me
everything is ok, but when I tried to ext2resize the filesystem, I got a 
segmentation fault.

Re: [linux-lvm] snapshots not stable with 2.3.99pre2

[Richard Heider jr.]

Jan Niehusmann schrieb:

> While testing lvm with linux 2.3.99pre2 I had 2 crashes while trying out snapshots.
> Without snapshots lvm seems to be stable.

When snapshots were mentioned the other week, I tried finding something in the docs,
but I couldn't.
Could someone please give me a reference on what snapshots are and how they work - or
is it "RTF..Source" ?-)

cu
Richard
--
Richard Heider jr.                            http://www.heider.de/

Re: [linux-lvm] snapshots not stable with 2.3.99pre2

[Jan Niehusmann]

On Wed, Mar 22, 2000 at 06:39:24PM +0100, Richard Heider jr. wrote:
> When snapshots were mentioned the other week, I tried finding something
> in the docs, but I couldn't. Could someone please give me a reference
> on what snapshots are and how they work - or is it "RTF..Source" ?-)

Snapshots are virtual copys of logical volumes. Such a copy is read only
and doesn't change when you write to the cloned volume. 

This is often used for backups: If you backup a filesystem while 
it's in use, you may end up with an inconsistant or incomplete backup.
(after you wrote the first half of your filesystem to tape, someone moves
a file from the second half to the first one, so you miss it when you write
the second half to tape, for example.)
If you have snapshots, you create the snapshot at one moment and then 
write the (read only) snapshot to tape.


Jan

Re: [linux-lvm] snapshots not stable with 2.3.99pre2

[Heinz Mauelshagen]

> While testing lvm with linux 2.3.99pre2 I had 2 crashes while trying out snapshots.
> Without snapshots lvm seems to be stable.

Investigating in the area of trouble with 2.3.99pr2 kio support...

> 
> Another problem is (probably) a missing check in lvextend: I tried to extend a
> striped lv, and while I had enough space available, nearly all this space was on
> one pv, so it was not possible to create a correctly striped volume with the 
> extended size. But I didn't get the error message I expected: lvextend told me
> everything is ok, but when I tried to ext2resize the filesystem, I got a 
> segmentation fault.
> 
> 

Could you provide more configuration information by "vgdisplay -v" on the
involved VG, a "lvextend -d" stdout/stderr and an "strace ext2resize" of your
try, please.

Do you get any segfaults when you just read/write to the extended part
of the Logical Volume with dd?

Heinz
-- 

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Systemmanagement CS-TS                           T-Nova
                                                 Entwicklungszentrum Darmstadt
Heinz Mauelshagen                                Otto-Roehm-Strasse 71c
Senior Systems Engineer                          Postfach 10 05 41
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