Re: [Evms-devel] Possible to create a degraded RAID5 array with EVMS?

[Steve D. <st...@us...>]

"James Lee" <jam...@ho...> wrote on 11/18/2005 05:52:35 PM:

Hi, James.

> Well I've tried doing this again, this time using the standard Linux
> partition types.  I started by wiping all the partitions on the drive
(using
> cfdisk).  I then created the new partitions with cfdisk, and loaded up
EVMS
> to make sure it was OK (I hadn't tried to create any RAID volumes yet).
>
> EVMS comes up with some warnings about not being able to assemble some
RAID
> arrys.  These arrays should not longer exists; I don't know where EVMS is

> picking them up from?  Do I need to do something more than just wiping
> partitions to get rid of RAID information on a drive?  Or does EVMS store

> configuration in a config file rather than redetecting it each time?

The metadata for MD devices is stored near the end of the device.  (Round
the end of the device down to a 64KB boundary, then put the metadata at the
start of the 64KB block just before the previously calculated 64KB
boundary.)  My guess is that you recreate the partitions to be the same
size.  EVMS then found the leftover MD metadata at the end of the
partitions.

> Anyway, EVMS then gets very confused about these RAID arrays, and on
exiting
> I get the following error (and the process hangs):
>
> *** glibc detected *** corrupted double-linked list: 0x081a88a0 ***
>
> I've attached the debug information for this.  Hopefully it might prove
> helpful.

Judging from the last lines in the log, it looks like it got tripped up on
a free().  (Different place in the code that the previous log you sent, but
on a free() nonetheless)  However, the log is missing the debug information
for the memory allocations.  Did you rebuild EVMS after running
"./configure --with-debug <your-other-options>"? The debug version of the
memory allocation code should catch a double free.  Did you run with the
debug level set to "everything" (e.g., "evmsgui -d everything")?  It would
be helpful to have the history of memory allocations and frees in the log.

> I have to say I'm somewhat concerned about these errors.... how
> stable is the RAID5 code in EVMS considered compared to, say, mdadm?
Don't
> get me wrong though, I'm very impressed with EVMS overall :)

The EVMS MD plug-in went through a significant overhaul in order to add
support for the version 1 MD superblock.  Naturally, some stability was
lost in the rework.  The bugs are being found and fixed.

Steve D.