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

[James L. <jam...@ho...>]

>From: Mike Tran <mh...@us...>
>To: evm...@li...
>Subject: Re: [Evms-devel] Possible to create a degraded RAID5 array 
>with	EVMS?
>Date: Tue, 29 Nov 2005 18:50:34 -0600
>
>Mike Tran wrote:
>
>>On Sat, 2005-11-26 at 14:42, James Lee wrote:
>>
>>
>>>Hi there,
>>>
>>>I'm having some more trouble with getting EVMS and mdadm to play nicely 
>>>together (even after upgrading EVMS)...
>>>
>>>The steps I'm taking are:
>>>
>>>1. Starting with an empty drive (wiped it by zero-filling the start and 
>>>end of drive to make sure there's no residual partition table 
>>>information).  Create two logical partitions (/dev/sdb5 and /dev/sdb6).
>>>
>>>2. Use mdadm to create a degraded "3-drive" RAID5 array called /dev/md0: 
>>>"mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/sdb5 /dev/sdb6 
>>>missing".
>>>
>>>3. Start EVMS.  It correctly detects the degraded RAID5 array on 
>>>/dev/md0.
>>>
>>>4. In EVMS, create 4 partitions on /dev/sdb, each one just over half the 
>>>size of the partitions in the RAID5 array.  Create two 2-drive RAID0 
>>>stripes, from these partitions.
>>>
>>>5. Add one of these RAID0 arrays to the RAID5 array.  Wait for it to 
>>>resync.  RAID5 array is now active and non-degraded.
>>>
>>>6. Create an EXT3 filesystem and bung some files on it.
>>>
>>>7. Everything working fine so far.  Now expand the RAID5 array with the 
>>>other RAID0 array.  This seems to work fine.  No data lost on the 
>>>partition and no errors.
>>>
>>>8. Reboot.  When next starting EVMS, I get the following errors:
>>>
>>>
>>>
>>
>>In theory, this should work!!! I will try your scenario to find out what
>>went wrong.
>>
>>
>>
>I could not reproduce this problem using evms 2.5.3.  Did you wait for the 
>raid5 expand to complete before rebooting the machine?
>
>--
>Mike T.
>

Thanks for looking into this Mike.  Yes, the RAID5 expand had completed 
successfully (and the machine was idle for a few hours before rebooting, 
with the array working fine).

Is it possible that these problems are caused by having some residual 
superblock left over from a previous array?  To save time, I wiped the drive 
by doing a wipe of the first and last million sectors of the drive (rather 
than zeroing the entire 320GB, which takes several hours).  Maybe I should 
try with a completely clean drive.

The version of mdadm I'm using doesn't support version 1 superblocks AFAIK, 
which is why I've had to use the older version 0.9 superblocks.  I can't see 
myself having more than 27 devices in this array, or moving it over to a 
byte-swapped (i.e. Sparc?) machine, so I should be OK.  Presumably support 
for the older superblock will continue into the future?