[linux-lvm] System locks solid under LVM

[Tony Rogers]

Hello everyone,

My difficulties with LVM
========================
Overview
--------
I have been playing with LVM for some time now, with mixed results. I
have a machine at work which has LVM 0.6 installed. Although this is
not utilised heavily, it works fine.

On the other hand, I have a machine at home, also using LVM 0.6, which
has SERIOUS problems. In simple terms, the computer locks solid when
it comes under moderate load. I can trigger this VERY easily, but
don`t know how best to debug the situation.

I have just joined the mailing list, and noticed some mention of lock
ups, but the feeling seemed to be that if the underlying system was
OK, the LVM should be fine. I`m not convinced that this is true in my
case.

As is usual with hobby configurations, I have lots of I/O cards installed,
and have done my best to eliminate hardware / other system causes  as a
source of the problem.

My configuration
----------------
I am using Redhat 5.2, initially with Kernel 2.0.36, but have now
upgraded to 2.2.2 in an attempt to get the latest drivers for my hardware.

I have two Ethernet cards (ISA & PCI), two SCSI cards (ISA & PCI), a
sound card (ISA) and a video card (PCI).

The SCSI controller is a Diamond Fireport 40, and it is this
controller which hosts two partitioned Fireball 6.4G drives. It is
parts of these drives which have LVM configured for them.

Detailed description
--------------------
Because it is so easy to push the system over, I decided that I needed
to find out how to make the system stable again!

I now have two Kernels to play with. Both are 2.2.2, one with LVM
built in, and the other without the LVM patches.

This allows the following three scenarios:
1) Clean kernel - No LVM of any kind.
2) LVM Kernel - Not using LVM.
3) LVM Kernel - Using LVM.

In order to load the system, all I do is copy the contents of one
filesystem to that on another partition, either native ext2 or ext2 on
a Logical Volume (depending on the test).

My LVM configuration is as follows:

One Volume Group comprising 4 PVs on 2 SCSI drives. There are 7
Logical volumes in this group, but I do my testing on one of ~1.5G capacity.

I experimented with striping the LVs, but decided to settle on a
`straight` linear LV for the purposes of the tests.

The results of my testing (over a couple of weeks) seem to show the
following:

Case 1 - Clean Kernel. Solid, even with two simultaneous bulk copies
AND an archive to tape, at the same time.

Case 2 - LVM Kernel - Not using LVM. Pretty solid. A couple of  lock ups.

Case 3 - LVM Kernel - Using LVM. Falls over almost every time within
seconds or minutes. It lasted over an hour once only.

Plea for help
-------------
I really want to keep using LVM (it is the way forward!), and am
prepared to make quite some effort to make it work for me.

The problem I have, is that the machine seems to lock SOLID with no
warning, and there are no errors (that I can see) available to look
at.

I really am stuck. Is there any debugging that I can enable?

Any help will be appreciated, and I am willing to post any fix, for
the benefit of the list.

Thanks in advance, and sorry for the long mail!

Tony Rogers
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